Opal and chalcedony formation debate
May 28, 2024 22:23:22 GMT -5
RWA3006, opalpyrexia, and 3 more like this
Post by vegasjames on May 28, 2024 22:23:22 GMT -5
The following is a debate I had on opal and chalcedony formation on another rock board. Has a lot of good information and shows how some people refuse to let go of false beliefs despite overwhelming evidence to the contrary. So, I decided to post it here.
I was pointing out that chalcedonies (cryptocrystalline to microcrystalline quartz) are the dehydration product of opals. Chalcedonies DO NOT spontaneously form. It is a transition process in which the dissolved silica first condenses in to a gel forming opal before losing sufficient water to crystallize in to a chalcedony (common chalcedony, agate, jasper, chert/flint).
A supposed "geologist" jumped in and started arguing. He made so many basic mistakes and contradicted himself so many times, even saying the same things as fact that I had already explained to him that he was telling me was false originally.
He also erroneously claimed that opals and chalcedony require high temperatures and high pressure to form, which again is false. Some opals can form from solutions or silica rich gases that initially hot, but cool rapidly, which is why chalcedonies have such tiny crystal structure. Crystals formed from heat grow larger when cooled slower. Opals and the resultant chalcedonies formed in the Earth, form at shallow, cool levels. Opals also form deep in the oceans where temperatures reach close to freezing.
The debate:
Response of James Sloane to Benjamin McCann: Actually all chalcedonies are the dehydration product of opals. So, the difference is really opal is amorphous, contains water and has a lower density. Chalcedonies are cryptocrystalline to microcrystalline, has little to no water as part of the structure and has a higher density.
Response of James Sloane to Lily Hayes Eisele: Yes, as I pointed out, chalcedonies do not spontaneously form. They will only form as the opal loses sufficient water leading to crystallization. I have a shorter write up on this that may be easier to follow: “I posted this on another board in response to post with various misinformation such as claiming agate is amorphous like opal and that opal is a chalcedony. Figured I would post my response in a few places to help educate people on the topic of opal vs chalcedonies and formation:
"Opal is not a chalcedony. Opal converts in to a chalcedony. Chalcedonies are microcrystalline or cryptocrystalline quartz. Both cryptocrystalline and microcrystalline are in essence the same thing in the fact that the crystals are so small that they cannot be seen with the naked eye. The only difference is that under microscope magnification the crystals of microcrystalline quartz can be differentiated. Cryptocrystalline quartz crystals on the other hand are so small that under microscope magnification the crystals cannot be differentiated. There are actually around 300 types of opal, and not all are stones. The stingers of bees and of nettle plants are covered with opal. And bamboo sap, which is super high in silica, can form a type of opal called "vegetable opal". Opals we refer to stones though start out from saturated to supersaturated silica solutions. I won't bother going in to a ton of details, but the silica molecules are attracted towards each other through forces known as van der Waals forces. As these molecules move closer together, water is squeezed out forming a solid amorphous (no crystalline structure) gel. When the water content reaches as average of 3-21% the result is opal, which again is not a true solid, but rather a solid gel. As opal continues to lose water, below 3%, the opal converts from an amorphous gel, to some form of chalcedony (common chalcedony, agate, jasper or chert/flint) all of which are microcrystalline or cryptocrystalline quartz (silicon dioxide), none of which are amorphous since they all have crystal structure unlike opal. What form of chalcedony the opal with take will depend on the silica source. Agates and common jaspers are formed from inorganic silica sources such as sandstone or clays. Chert/flint is produced from opal created from silica derived from the biogenic sources of diatoms and radiolarians. Opal varies quite a bit in hardness and stability for a couple of reasons. One is water content. The higher the water content of opal the softer it is, as well as the less stable it is. The stability issue goes back to the fact that opal is not a true solid, but rather a solid gel. Therefore, it does not really have a stable structure. As water is lost from the opal, the gel much restructure to gain some sense of stability. If water is lost from the opal too rapidly, then the opal does not have the time to properly restructure and the opal will form cracks (craze). To stabilize high water content opals, the water content much be very slowly reduced over 6 months to years out of light and with a fairly consistent temperature. The second factor is aluminum oxide content. Most people think opals are just pure silicon dioxide and water, which is very rarely the case. Opals can contain various other elements and compounds such as uranium, barite. The primary other component of most opal though is aluminum oxide. The aluminum oxide content to opal affects not only its density, but also hardness that both increase with increasing aluminum oxide content. The aluminum oxide is mainly derived from clays, but can also come from other sources such as diatoms. As a final note, contrary to what is commonly taught, opal does not take millions of years to form. The formation of opal has been shown to rather rapid, and can be grown and stabilized in as little as a year. Its conversion in to chalcedonies such as agate or jasper does take significantly more time."
Response of Benjamin McCann to James Sloane: James Sloane you latched on to the opal and quartz are 2 different things and ran. The chemistry is the same. The deposition is not.
For those in the back, Opal is hydrated silica and tends to form In depositional locations that are usually close to the surface with higher than normal water and heat than the surrounding region. The heat and water convert the SiO2 into SiO2 • nH2O and after the depositional event, the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe.
However, Chalcedony is a GENERIC term for all micro- to cryptocrystalline quartz. It’s deposited through sedimentation, volcanics and metamorphic processes, and is frequently the last fluid to mineralize as the leftover from magmatic deposition.
So let’s correct you, all opal converts to chalcedony, not all chalcedony is from opal. Get that logical fallacy right out of here.
You’re arguing deposition and mineralogy with an economic geologist that has has studied flash deposition of vapor like fluids under pressure in the reactivation of extinct fault lines.
Mostly involving carlin type gold deposits. Which exist only in Nevada. Where I studied geology.
Your silica variant descriptions have not been accurate since before 2008.
And this is why continuing education is important so you stop spreading misinformation that has not been correct in over 20’years.
Response of James Sloane to Benjamin McCann: I latched on to the fact that opal and quartzes are not the same thing because they are not the same thing. Tell me, would you pay $1,000 a carat for a charcoal briquette or graphite since chemically they are identical to diamond and thus according to your faulty reasoning that would make charcoal and graphite diamonds? Being chemically the same, which opal and quartz are not to begin with does not make them the same thing. As another example, calcite, marble, aragonite and coral are all calcium carbonate. So, are these all calcite to you? Or are they all marble, aragonite or corals to you? See why your reasoning is so faulty yet? Opal and quartz do not even have the same chemistry. Opal is silicon dioxide, usually aluminum oxide and water. Quartz is silicon dioxide. That right there already proves to us that opal and quartz ARE NOT the same thing. Further differentiating the fact that opal and quartz ARE NOT the same thing is the fact that opal is amorphous as where all forms of quartz are crystalline. And the fact that opal is not a true solid, but rather a solid gel with water as part of its structure, as where quartz is a true solid lacking any water as part of its structure. As we can see with all the evidence, opal and quartz are 100% NOT the same thing. Then you write "Opal is hydrated silica and tends to form In depositional locations that are usually close to the surface with higher than normal water and heat than the surrounding region. The heat and water convert the SiO2 into SiO2 • nH2O and after the depositional event, the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe. " To start with, you are contradicting yourself here. You claim opal forms near the surface, which is kind of true. Opal can form on the surface, or just below the surface with a maximum averaging 30-40 feet below the surface. This shallow of a depth does not produce sufficient heat to have any significant alteration of the silica and the water. For example, quartz, which again is not opal, forms at much greater depths and temperatures where the water becomes supercritical allowing it to dissolve the silica, where it then becomes supersaturated and crystallizes out upon cooling. Almost all opal on the other hand forms under low to very low temperatures. For example, precious opal has a play of color. The colors depend on the temperature of formation. Red for example forms at near freezing temperatures. The only opal that may form at higher temps is hyalite opal, which is a volcanic opal, but I have not looked in to it to see if the silica rich volcanic water is injected first in to cooler layers before opalization occurs. Then you repeat at the end of that statement that the opal dehydrates in to chalcedony, which was the fact that I first pointed out and you claimed I was wrong. So, you are finally admitting that contrary to your claim, I was 100% correct all along. Same with my point that chalcedony is a cryptocrystalline to microcrystalline quartz as I kept pointing out, but you kept incorrectly claiming that chalcedony was only a microcrystalline quartz, which is very different from opal. So, you really want to keep arguing while you prove everything I am saying is correct?
Going to add that there are actually organic sources of opals such as bamboo opal, and the tips of stinging nettle leaves and bee stingers are covered with opal. Therefore, based on your hypothesis of opal forms near the surface with the above normal heat converting the silica in to silica and water, which by the way is impossible since silica nor heat contain hydrogen to form water, how do these opals form? And if you are a geologist and since you brought up the Carlin gold deposits, then you should know that the Carlin gold is microscopic that was formed several kilometers below the Earth's surface where again supercritical water plays a role that is a super solvent. Why is this important? Well, it is well known to play a role in the formation of quartz, which again is crystalline, not amorphous like opal. And supercritical water also plays a role in the dissolving of gold, which is why gold is often found with quartz. Although, it is also well known that supercritical fluids do not form near the surface of the Earth and definitely not in the shallow depths in which opal, which again is not quartz, forms. This is all super basic science. And since you are still incorrectly claiming that chalcedonies are not all the dehydration product of opal, although you then contradicted your claim again by repeating what I already educated you on where you wrote "the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe. " Therefore, instead of debunking my claims, you are proving my claims correct and even admitting I am right while still trying to argue those same claims are wrong. So, how about you explain to everyone here how chalcedony, which forms at shallower depths and not in supercritical water like macrocrystalline quartz does spontaneously forms as it would have to do if not a dehydration product of opal.
Response of Benjamin McCann to James Sloane: James Sloane you flat out said all chalcedony is from opal. And not even a majority of chalcedony is from opal in reality. Silca is generally the second most abundant fluid behind water in melts as long as were not talking mafic minerals.
So far I’ve seen a lot of cut and paste sound bites from the internet that agree with you but don’t actually disprove anything I’ve said.
Also funny you mention calcite and aragonite since they are chemically identical but have a different cell structure from differences in deposition and crystal growth, literally the same principles that affect differences between quartz and opal.
Let’s do some basic chemistry.
Silca: SiO2
Opal: SiO2 • nH2O.
Opal + pressure/heat/time: SiO2 + nH20
Aluminum oxide is not part of the structure, it’s trace minerals caught in the lattice, which has the space exactly because of the extra H2O.
Opal is a mineraloid. It’s not the end product. It will dehydrate until what is left is silica.
So enjoy arguing chemistry and how they are different and not the same when they both exist in a triple point graph of SiO2. You don’t need just depth or temperature, you need the combination that creates the pressure for supercritical fluids, which can occur way more shallow than you seem to believe.
Your whole point has been how all chalcedony comes from opal. Flat out not true. I’d never pay $1000 a carat for any form of carbon because yes they are all the same after you treat them with heat and pressure. I’ll happily take the 1/3 cost lab grown with less inclusions that DIDN’T come from a blood mine. Because chemically a diamond from the earth is the same as one from the lab.
Response of James Sloane to Benjamin McCann: Benjamin McCann Here, I am going to help you out: www.sciencedirect.com/.../abs/pii/0016703777900990 "Evidence from deep-sea sediments supports the following diagenetic maturation sequence: opal-A (siliceous ooze) → opal-CT (porcelanite) → chalcedony or cryptocrystalline quartz (chert)."
Response of Benjamin McCann to James Sloane: James Sloane Carlin type is microscopic gold that got caught in the lattice of pyrite crystals during flash vaporization of fluids during the reactivation of thrust faults as normal faults. The depth is a function of the faults not the vaporization. If you would really like to know about carlin type gold deposits in the extensional region of the great basin I recommend you look up Jean Cline.
As for how “chalcedony” forms, it literally runs the width and breadth of mineralogy because it IS the second most common fluid in melt after water. Basic science as you said.
Response of Benjamin McCann to James Sloane: James Sloane literally one type. You give me one deposition type and call it a day. Would you like to hear the difference in deposition between ocean sediments and porphyry deposits? Because that’s the width and breadth I’m talking about. You take a deep sea diagenesis and try to say that explains everything.
Please read articles before sharing them thinking they prove your point. The introduction even explains its redeposition.
Response of James Sloane to Benjamin McCann: www.mdpi.com/2075-163X/10/11/1037 "Calculations based on fluid inclusion and oxygen isotope studies point to a range between 20 and 230 °C for agate formation temperatures. The accumulation and condensation of silicic acid result in the formation of silica sols and proposed amorphous silica as precursors for the development of the typical agate micro-structure. " Hmm, amorphous silica, such as opal, a precursor for agate formation. And look at the temperatures for agate formation, which are far too low for the supercritical temps required for macrocrystalline quartz formation. proving that agate forms at the lower temps associated with opal formation, not macrocrystalline quartz formation.
Response of James Sloane to Benjamin McCann: Benjamin McCann Funny you should harp on deep sea diagenesis as this is how chert/flint from opal forms. And it does not require the high heat you claimed earlier is required as it is actually quite cold at those depths. In fact, diagensis is a low pressure and low temperature process unlike metamorphism. I love when people contradict their own claims. Makes debating them so much easier. Oh, by the way, along these lines from one of the studies I collected as part of my opal production experiments agupubs.onlinelibrary.wiley.com/.../ME003p0315 "In general, silica diagenesis proceeds as a maturation from biogenic opal (opal-A)→ opal-CT→ quartz." As we can clearly see opal will eventually form in to a quartz, or in this case the chalcedony (quartz) known as chert or flint. This also once again proves that opal and quartz ARE NOT the same thing as you keep incorrectly claiming among your numerous other errors.
Response of James Sloane to Benjamin McCann: Benjamin McCann The fact that you posted a laughing emoji on my serious post says it all. This is the adult equivalent of throwing a temper tantrum when you are told no. If you were debating instead of being childish, then you would post evidence to your claims like I have. What is even funnier is how you told me I was wrong and you posted clearly incorrect information as you continue to do, then when I correct you, instead of admitting you were wrong to begin with, you simply change your wording to fit the facts I pointed out and post statements agreeing with what I already aid that you originally claimed I was wrong on.
Response of Benjamin McCann to James Sloane: James Sloane you flat out said all chalcedony is from opal.”
Response of James Sloane to Benjamin McCann: Yes, because this is true. This is why you cannot answer how chalcedonies supposedly spontaneously form, which you would need to do to evidence your hypothesis.
Response of Benjamin McCann to James Sloane: “And not even a majority of chalcedony is from opal in reality”
Response of James Sloane to Benjamin McCann: Only according to you. Not according to science. And you have still failed to provide any evidence to your claim. You just keep repeating the same misinformation as “fact’. If you are really a geologist, then you should know this is not how science works.
Response of Benjamin McCann to James Sloane: “Silca is generally the second most abundant fluid behind water in melts as long as were not talking mafic minerals. “
Response of James Sloane to Benjamin McCann: Silica is not a fluid to begin with, and dissolved in water, silica forms silicic acid, which is not the same as silicon dioxide. So again, you are proving your lack of knowledge on the subject.
Response of Benjamin McCann to James Sloane: “So far I’ve seen a lot of cut and paste sound bites from the internet that agree with you but don’t actually disprove anything I’ve said. “
Response of James Sloane to Benjamin McCann: Actually, what you are seeing is called evidence, something you have yet to present yourself. You just keep making erroneous and unfounded claims, then claim I am wrong while you change your wording after claiming I am wrong to say the same things I already told you and corrected you on.
And yes, the evidence proves you wrong if you actually read it, and understand it.
This also explains why you keep evading answering my question for you of how chalcedony spontaneously forms. You won’t answer because your answer would only further prove my statements of fact while proving your unfounded claims wrong.
Response of Benjamin McCann to James Sloane: “Also funny you mention calcite and aragonite since they are chemically identical but have a different cell structure from differences in deposition and crystal growth, literally the same principles that affect differences between quartz and opal. “
Response of James Sloane to Benjamin McCann: First of all rocks do not have cells. You are confusing biology with geology.
And, yes, calcite and aragonite have different crystal structures. That was the whole point of what I was telling you. You erroneously claimed that quartz and opal are the same thing because they both contain silicon dioxide, which technically is still incorrect as silicon dioxide is a misnomer. That gets too complicated for the average person though so we will stick to silicon dioxide. Anyway, as I pointed out so many times to you, just because something has the same chemicsty, or in the case of quartz and opal, which have similar chemistry, this DOES NOT make them the same thing, Again, marble, calcite and aragonite all have the same chemistry but different crystal structures making them DIFFERENT minerals. Just like graphite and diamond are both carbon but still different minerals. Same as glucose, fructose, idose, mannose, sorbose, allose and many other sugars are C6H1206, but are all different sugars. Point is again, that simply having the same atoms in the same ratio does not make all substances with the same atoms and same ratio all the same material. Anyone with even 6th grade level of education in science should know this fact. Therefore, just because quartz is composed of silicon dioxide and opal is composed on silicon dioxide and water this DOES NOT make them the same thing as you keep erroneously stating. Again, quartz is a true solid as where opal is a solid gel. Quartz does not contain water as part of its structure as where opal does. Quartz is macrocrystalline as where opal is amorphous. Quartz forms deep in the Earth under intense pressure and heat out of supercritical water. Opals on the other hand form at lower temperatures, at shallow depths or at the surface in much shorter periods of time than it takes for opal to form. So once again you are wrong, quartz and opal ARE NOT the same thing,
Response of Benjamin McCann to James Sloane: “Let’s do some basic chemistry.
Silca: SiO2”
Response of James Sloane to Benjamin McCann: Again, not quite true, but we do not need another debate right now when I am still disproving your claims in this debate.
Response of Benjamin McCann to James Sloane: “Opal: SiO2 • nH2O.”
Response of James Sloane to Benjamin McCann: Very good. Now what is the formula for quartz? Is it identical to opal that you claim is the same thing? I will you save you the time and having to type two letters. The answer is NO!!!
Response of Benjamin McCann to James Sloane: “Opal + pressure/heat/time: SiO2 + nH20”
Response of James Sloane to Benjamin McCann: What? Now you are saying opal forms opal? Opal, which as you pointed out is SiO2 + nH20 with pressure, heat and time forms opal? No, opal again forms under low pressure, low temperatures and actually takes very little time. As the opal loses water below a 3% concentration, then the opal goes from an amorphous structure to a crystalline structure as it converts in to chalcedonies.
Response of Benjamin McCann to James Sloane: “Aluminum oxide is not part of the structure, it’s trace minerals caught in the lattice, which has the space exactly because of the extra H2O. “
Response of James Sloane to Benjamin McCann: First of all, I never said part of the structure. Although, your argument can be easily debated.
I will start with the fact that the silicic acid does not simply spontaneously form in to a gel. It requires a nucleator, which can be a variety of things such as uranium, barium, aluminum, etc. The nucleator is the basis for the “scaffolding” and this is linked to the silicic acid molecules. Thus, they ARE part of the lattice structure.
Secondly, you claim that the aluminum oxide is a trace mineral caught in the lattice for which again you provide no evidence. As pointed out, the aluminum can be a nucleator and thus part of the structure and not simply “caught in the lattice” as you claim, and the level of aluminum oxide that may or may not be present varies a lot in opals. This means it may not be present at all if the silicic acid was derived from a silica source without aluminum oxide, or the opal may have trace or higher levels of aluminum depending on the aluminum content of the silica source for the silicic acid. This is one of the factors that affects the varying density of opals, and is a factor that determines the variability in opal hardness. Higher levels of aluminum oxide in opals can increase both density and hardness. Just so you know, opals to not have a specific density or hardness. They have a narrow range of density and hardness.
Response of Benjamin McCann to James Sloane: “Opal is a mineraloid.”
Response of James Sloane to Benjamin McCann: Wow, thanks for once again repeating exactly what I already explained to you about opal being a mineraloid instead of a mineral.
Response of Benjamin McCann to James Sloane: “It’s not the end product.”
Response of James Sloane to Benjamin McCann: Again, thank you for once again repeating exactly what I already explained to you multiple times. Although, you really do not need to keep repeating exactly what I already educated you on. I already know this stuff extremely well, and my memory for this stuff is great. Therefore, you really do not need to keep telling me what I just got done teaching you.
Response of Benjamin McCann to James Sloane: “It will dehydrate until what is left is silica. “
Response of James Sloane to Benjamin McCann: Yes, again just as I already explained to you multiple times!!! The opal dehydrates in to the silica known as chalcedonies, which is a cryptocrystalline to microcrystalline quartz unlike the amorphous and water containing opal.
Response of Benjamin McCann to James Sloane: “So enjoy arguing chemistry and how they are different and not the same when they both exist in a triple point graph of SiO2”
Response of James Sloane to Benjamin McCann: I cannot believe you still do not get such as super simple fact of science. Simply having the same atoms, which opal and quartz DO NOT, does not make different things the same. I have explained this to you so many times and cannot simplify these facts any more than I have.
Response of Benjamin McCann to James Sloane: “You don’t need just depth or temperature, you need the combination”
Response of James Sloane to Benjamin McCann: Thank you for once again repeating exactly what I already just got done educating you about. I pointed out the fact the supercritical water needed to form quartz, but not opal, which is not the same as quartz as you keep incorrectly claiming, requires sufficient pressure AND temperature. Again, you really do not have to keep repeating everything I have already educated you on.
Response of Benjamin McCann to James Sloane: “that creates the pressure for supercritical fluids, which can occur way more shallow than you seem to believe. “
Response of James Sloane to Benjamin McCann: I am going to make this really easy. Show everyone here scientific evidence that supercritical fluids form NATURALLY at the surface or within 40 feet of the surface of the Earth as this is the range in which opals, which is the topic, not quartz that is something different, is formed. This ought to be fun, although I suspect you will realize your mistake I am calling you on, and you will avoid trying to provide the non-existent evidence to your claim.
Response of Benjamin McCann to James Sloane: “Your whole point has been how all chalcedony comes from opal. Flat out not true”
Response of James Sloane to Benjamin McCann: This coming from the guy who also claims opal and quartz are the same thing, which is not true. And that thinks opal converts in to opal. And who also erroneously refers to silica as a “fluid”. And that wrote “Opal is hydrated amorphous quartz”. Quartz is crystalline, the OPPOSITE of amorphous. So, opal cannot be crystalline like quartz if is amorphous. Therefore, they ARE NOT the same thing as I explained over and over to you. On top of that, even you wrote “all opal converts to chalcedony” AFTER I had already explained this fact to you. Of course, you also kept writing that chalcedony was only microcrystalline quartz until I corrected you a couple of times that it can be cryptocrystalline to microcrystalline, at which point you once again changed your wording without ever admitting to the fact you were wrong again. Therefore, right now you have very little credibility. You have your chance though to redeem yourself. Simply show everyone here the scientific proof of supercritical water formation naturally at surface level to 40 feet deep in the range of opal formation, unless you were just making crap up again.
Response of Benjamin McCann to James Sloane: “I’d never pay $1000 a carat for any form of carbon because yes they are all the same after you treat them with heat and pressure. I’ll happily take the 1/3 cost lab grown with less inclusions that DIDN’T come from a blood mine. Because chemically a diamond from the earth is the same as one from the lab.”
Response of James Sloane to Benjamin McCann: So, you would be willing to pay roughly $333 per carat for a piece of carbon when you can get a bag full of charcoal briquettes for around $10 that is also carbon? Seems pretty silly to me since you think having the same chemistry makes something the same thing. If you have a significant other, try giving them a ring with a mounted charcoal briquette and see if they agree with you that same chemistry makes that charcoal briquette the same as diamond. Then maybe you will finally understand my point, and why you are again wrong.
And if lab grown diamonds are exactly the same as naturally mined diamonds, then why are lab grown diamonds well known for reacting stronger to fluorescent lighting and fluoresce longer than naturally mined diamonds? If they are exactly the same, then they should react exactly the same. By the way, one of my projects I am working on is low pressure diamond synthesis, so I am well versed on diamonds and their structures and formation as well. So, if you wish to debate diamonds after I finish educating you on opals, we can start a new thread.
By the way, not all mined diamonds are blood diamonds. Diamonds are found in various places around the world and are even mined here in the United States and in Canada. So, you really think those are blood diamonds?
You keep making these false accusations that I am wrong then repeat what I already educated you on as fact. Now you are claiming that the studies I am posting do not support my position, which is also false. This is why you cannot provide any evidence to the contrary including you cannot quote anything in these abstracts that prove my claims wrong because as usual, you are just making crap up to try and save face after being totally discredited.
Response of James Sloane to Benjamin McCann: Since Benjamin McCann still does not understand the geology of chalcedony formation, I have yet another study for him. Prior study I posted already went to in to biogenic silica in ocean water forming opal then converting in to the chalcedony chert/flint. What is the other major chalcedony? Agate. So, let's take a look at agate formation. www.researchgate.net/publication/233648978_The_formation_of_agate_structures_Models_for_silica_transport_agate_layer_accretion_and_for_flow_patterns_and_flow_regimes_in_infiltration_channels The silica gel being referred to has to convert in to opal before it can convert in to chalcedony. This is why I keep asking Benjamin McCann to explain how chalcedonies supposedly spontaneously form from silica as he implies, which he keeps evading because that is not how things work. The recycled solvent in the gel referred to in the study is water. Again, as water is lost from the silica solution a gel is formed first. As the water content drops below 24%, the result is opal formation, which again is a solid silica gel with amorphous structure. When enough water is finally lost from the opal gel (below 3%), the opal then starts to crystallize in to a layer of chalcedony. As this process keeps repeating, alternating colored bands of chalcedony form resulting in agate formation.
Response of James Sloane to Lily Hayes Eisele: Yes, as I pointed out, chalcedonies do not spontaneously form. They will only form as the opal loses sufficient water leading to crystallization. I have a shorter write up on this that may be easier to follow: “I posted this on another board in response to post with various misinformation such as claiming agate is amorphous like opal and that opal is a chalcedony. Figured I would post my response in a few places to help educate people on the topic of opal vs chalcedonies and formation:
"Opal is not a chalcedony. Opal converts in to a chalcedony. Chalcedonies are microcrystalline or cryptocrystalline quartz. Both cryptocrystalline and microcrystalline are in essence the same thing in the fact that the crystals are so small that they cannot be seen with the naked eye. The only difference is that under microscope magnification the crystals of microcrystalline quartz can be differentiated. Cryptocrystalline quartz crystals on the other hand are so small that under microscope magnification the crystals cannot be differentiated. There are actually around 300 types of opal, and not all are stones. The stingers of bees and of nettle plants are covered with opal. And bamboo sap, which is super high in silica, can form a type of opal called "vegetable opal". Opals we refer to stones though start out from saturated to supersaturated silica solutions. I won't bother going in to a ton of details, but the silica molecules are attracted towards each other through forces known as van der Waals forces. As these molecules move closer together, water is squeezed out forming a solid amorphous (no crystalline structure) gel. When the water content reaches as average of 3-21% the result is opal, which again is not a true solid, but rather a solid gel. As opal continues to lose water, below 3%, the opal converts from an amorphous gel, to some form of chalcedony (common chalcedony, agate, jasper or chert/flint) all of which are microcrystalline or cryptocrystalline quartz (silicon dioxide), none of which are amorphous since they all have crystal structure unlike opal. What form of chalcedony the opal with take will depend on the silica source. Agates and common jaspers are formed from inorganic silica sources such as sandstone or clays. Chert/flint is produced from opal created from silica derived from the biogenic sources of diatoms and radiolarians. Opal varies quite a bit in hardness and stability for a couple of reasons. One is water content. The higher the water content of opal the softer it is, as well as the less stable it is. The stability issue goes back to the fact that opal is not a true solid, but rather a solid gel. Therefore, it does not really have a stable structure. As water is lost from the opal, the gel much restructure to gain some sense of stability. If water is lost from the opal too rapidly, then the opal does not have the time to properly restructure and the opal will form cracks (craze). To stabilize high water content opals, the water content much be very slowly reduced over 6 months to years out of light and with a fairly consistent temperature. The second factor is aluminum oxide content. Most people think opals are just pure silicon dioxide and water, which is very rarely the case. Opals can contain various other elements and compounds such as uranium, barite. The primary other component of most opal though is aluminum oxide. The aluminum oxide content to opal affects not only its density, but also hardness that both increase with increasing aluminum oxide content. The aluminum oxide is mainly derived from clays, but can also come from other sources such as diatoms. As a final note, contrary to what is commonly taught, opal does not take millions of years to form. The formation of opal has been shown to rather rapid, and can be grown and stabilized in as little as a year. Its conversion in to chalcedonies such as agate or jasper does take significantly more time."
Response of Benjamin McCann to James Sloane: James Sloane you latched on to the opal and quartz are 2 different things and ran. The chemistry is the same. The deposition is not.
For those in the back, Opal is hydrated silica and tends to form In depositional locations that are usually close to the surface with higher than normal water and heat than the surrounding region. The heat and water convert the SiO2 into SiO2 • nH2O and after the depositional event, the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe.
However, Chalcedony is a GENERIC term for all micro- to cryptocrystalline quartz. It’s deposited through sedimentation, volcanics and metamorphic processes, and is frequently the last fluid to mineralize as the leftover from magmatic deposition.
So let’s correct you, all opal converts to chalcedony, not all chalcedony is from opal. Get that logical fallacy right out of here.
You’re arguing deposition and mineralogy with an economic geologist that has has studied flash deposition of vapor like fluids under pressure in the reactivation of extinct fault lines.
Mostly involving carlin type gold deposits. Which exist only in Nevada. Where I studied geology.
Your silica variant descriptions have not been accurate since before 2008.
And this is why continuing education is important so you stop spreading misinformation that has not been correct in over 20’years.
Response of James Sloane to Benjamin McCann: I latched on to the fact that opal and quartzes are not the same thing because they are not the same thing. Tell me, would you pay $1,000 a carat for a charcoal briquette or graphite since chemically they are identical to diamond and thus according to your faulty reasoning that would make charcoal and graphite diamonds? Being chemically the same, which opal and quartz are not to begin with does not make them the same thing. As another example, calcite, marble, aragonite and coral are all calcium carbonate. So, are these all calcite to you? Or are they all marble, aragonite or corals to you? See why your reasoning is so faulty yet? Opal and quartz do not even have the same chemistry. Opal is silicon dioxide, usually aluminum oxide and water. Quartz is silicon dioxide. That right there already proves to us that opal and quartz ARE NOT the same thing. Further differentiating the fact that opal and quartz ARE NOT the same thing is the fact that opal is amorphous as where all forms of quartz are crystalline. And the fact that opal is not a true solid, but rather a solid gel with water as part of its structure, as where quartz is a true solid lacking any water as part of its structure. As we can see with all the evidence, opal and quartz are 100% NOT the same thing. Then you write "Opal is hydrated silica and tends to form In depositional locations that are usually close to the surface with higher than normal water and heat than the surrounding region. The heat and water convert the SiO2 into SiO2 • nH2O and after the depositional event, the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe. " To start with, you are contradicting yourself here. You claim opal forms near the surface, which is kind of true. Opal can form on the surface, or just below the surface with a maximum averaging 30-40 feet below the surface. This shallow of a depth does not produce sufficient heat to have any significant alteration of the silica and the water. For example, quartz, which again is not opal, forms at much greater depths and temperatures where the water becomes supercritical allowing it to dissolve the silica, where it then becomes supersaturated and crystallizes out upon cooling. Almost all opal on the other hand forms under low to very low temperatures. For example, precious opal has a play of color. The colors depend on the temperature of formation. Red for example forms at near freezing temperatures. The only opal that may form at higher temps is hyalite opal, which is a volcanic opal, but I have not looked in to it to see if the silica rich volcanic water is injected first in to cooler layers before opalization occurs. Then you repeat at the end of that statement that the opal dehydrates in to chalcedony, which was the fact that I first pointed out and you claimed I was wrong. So, you are finally admitting that contrary to your claim, I was 100% correct all along. Same with my point that chalcedony is a cryptocrystalline to microcrystalline quartz as I kept pointing out, but you kept incorrectly claiming that chalcedony was only a microcrystalline quartz, which is very different from opal. So, you really want to keep arguing while you prove everything I am saying is correct?
Going to add that there are actually organic sources of opals such as bamboo opal, and the tips of stinging nettle leaves and bee stingers are covered with opal. Therefore, based on your hypothesis of opal forms near the surface with the above normal heat converting the silica in to silica and water, which by the way is impossible since silica nor heat contain hydrogen to form water, how do these opals form? And if you are a geologist and since you brought up the Carlin gold deposits, then you should know that the Carlin gold is microscopic that was formed several kilometers below the Earth's surface where again supercritical water plays a role that is a super solvent. Why is this important? Well, it is well known to play a role in the formation of quartz, which again is crystalline, not amorphous like opal. And supercritical water also plays a role in the dissolving of gold, which is why gold is often found with quartz. Although, it is also well known that supercritical fluids do not form near the surface of the Earth and definitely not in the shallow depths in which opal, which again is not quartz, forms. This is all super basic science. And since you are still incorrectly claiming that chalcedonies are not all the dehydration product of opal, although you then contradicted your claim again by repeating what I already educated you on where you wrote "the opalised silica starts to dehydrate further until you are left with the Chalcedony you describe. " Therefore, instead of debunking my claims, you are proving my claims correct and even admitting I am right while still trying to argue those same claims are wrong. So, how about you explain to everyone here how chalcedony, which forms at shallower depths and not in supercritical water like macrocrystalline quartz does spontaneously forms as it would have to do if not a dehydration product of opal.
Response of Benjamin McCann to James Sloane: James Sloane you flat out said all chalcedony is from opal. And not even a majority of chalcedony is from opal in reality. Silca is generally the second most abundant fluid behind water in melts as long as were not talking mafic minerals.
So far I’ve seen a lot of cut and paste sound bites from the internet that agree with you but don’t actually disprove anything I’ve said.
Also funny you mention calcite and aragonite since they are chemically identical but have a different cell structure from differences in deposition and crystal growth, literally the same principles that affect differences between quartz and opal.
Let’s do some basic chemistry.
Silca: SiO2
Opal: SiO2 • nH2O.
Opal + pressure/heat/time: SiO2 + nH20
Aluminum oxide is not part of the structure, it’s trace minerals caught in the lattice, which has the space exactly because of the extra H2O.
Opal is a mineraloid. It’s not the end product. It will dehydrate until what is left is silica.
So enjoy arguing chemistry and how they are different and not the same when they both exist in a triple point graph of SiO2. You don’t need just depth or temperature, you need the combination that creates the pressure for supercritical fluids, which can occur way more shallow than you seem to believe.
Your whole point has been how all chalcedony comes from opal. Flat out not true. I’d never pay $1000 a carat for any form of carbon because yes they are all the same after you treat them with heat and pressure. I’ll happily take the 1/3 cost lab grown with less inclusions that DIDN’T come from a blood mine. Because chemically a diamond from the earth is the same as one from the lab.
Response of James Sloane to Benjamin McCann: Benjamin McCann Here, I am going to help you out: www.sciencedirect.com/.../abs/pii/0016703777900990 "Evidence from deep-sea sediments supports the following diagenetic maturation sequence: opal-A (siliceous ooze) → opal-CT (porcelanite) → chalcedony or cryptocrystalline quartz (chert)."
Response of Benjamin McCann to James Sloane: James Sloane Carlin type is microscopic gold that got caught in the lattice of pyrite crystals during flash vaporization of fluids during the reactivation of thrust faults as normal faults. The depth is a function of the faults not the vaporization. If you would really like to know about carlin type gold deposits in the extensional region of the great basin I recommend you look up Jean Cline.
As for how “chalcedony” forms, it literally runs the width and breadth of mineralogy because it IS the second most common fluid in melt after water. Basic science as you said.
Response of Benjamin McCann to James Sloane: James Sloane literally one type. You give me one deposition type and call it a day. Would you like to hear the difference in deposition between ocean sediments and porphyry deposits? Because that’s the width and breadth I’m talking about. You take a deep sea diagenesis and try to say that explains everything.
Please read articles before sharing them thinking they prove your point. The introduction even explains its redeposition.
Response of James Sloane to Benjamin McCann: www.mdpi.com/2075-163X/10/11/1037 "Calculations based on fluid inclusion and oxygen isotope studies point to a range between 20 and 230 °C for agate formation temperatures. The accumulation and condensation of silicic acid result in the formation of silica sols and proposed amorphous silica as precursors for the development of the typical agate micro-structure. " Hmm, amorphous silica, such as opal, a precursor for agate formation. And look at the temperatures for agate formation, which are far too low for the supercritical temps required for macrocrystalline quartz formation. proving that agate forms at the lower temps associated with opal formation, not macrocrystalline quartz formation.
Response of James Sloane to Benjamin McCann: Benjamin McCann Funny you should harp on deep sea diagenesis as this is how chert/flint from opal forms. And it does not require the high heat you claimed earlier is required as it is actually quite cold at those depths. In fact, diagensis is a low pressure and low temperature process unlike metamorphism. I love when people contradict their own claims. Makes debating them so much easier. Oh, by the way, along these lines from one of the studies I collected as part of my opal production experiments agupubs.onlinelibrary.wiley.com/.../ME003p0315 "In general, silica diagenesis proceeds as a maturation from biogenic opal (opal-A)→ opal-CT→ quartz." As we can clearly see opal will eventually form in to a quartz, or in this case the chalcedony (quartz) known as chert or flint. This also once again proves that opal and quartz ARE NOT the same thing as you keep incorrectly claiming among your numerous other errors.
Response of James Sloane to Benjamin McCann: Benjamin McCann The fact that you posted a laughing emoji on my serious post says it all. This is the adult equivalent of throwing a temper tantrum when you are told no. If you were debating instead of being childish, then you would post evidence to your claims like I have. What is even funnier is how you told me I was wrong and you posted clearly incorrect information as you continue to do, then when I correct you, instead of admitting you were wrong to begin with, you simply change your wording to fit the facts I pointed out and post statements agreeing with what I already aid that you originally claimed I was wrong on.
Response of Benjamin McCann to James Sloane: James Sloane you flat out said all chalcedony is from opal.”
Response of James Sloane to Benjamin McCann: Yes, because this is true. This is why you cannot answer how chalcedonies supposedly spontaneously form, which you would need to do to evidence your hypothesis.
Response of Benjamin McCann to James Sloane: “And not even a majority of chalcedony is from opal in reality”
Response of James Sloane to Benjamin McCann: Only according to you. Not according to science. And you have still failed to provide any evidence to your claim. You just keep repeating the same misinformation as “fact’. If you are really a geologist, then you should know this is not how science works.
Response of Benjamin McCann to James Sloane: “Silca is generally the second most abundant fluid behind water in melts as long as were not talking mafic minerals. “
Response of James Sloane to Benjamin McCann: Silica is not a fluid to begin with, and dissolved in water, silica forms silicic acid, which is not the same as silicon dioxide. So again, you are proving your lack of knowledge on the subject.
Response of Benjamin McCann to James Sloane: “So far I’ve seen a lot of cut and paste sound bites from the internet that agree with you but don’t actually disprove anything I’ve said. “
Response of James Sloane to Benjamin McCann: Actually, what you are seeing is called evidence, something you have yet to present yourself. You just keep making erroneous and unfounded claims, then claim I am wrong while you change your wording after claiming I am wrong to say the same things I already told you and corrected you on.
And yes, the evidence proves you wrong if you actually read it, and understand it.
This also explains why you keep evading answering my question for you of how chalcedony spontaneously forms. You won’t answer because your answer would only further prove my statements of fact while proving your unfounded claims wrong.
Response of Benjamin McCann to James Sloane: “Also funny you mention calcite and aragonite since they are chemically identical but have a different cell structure from differences in deposition and crystal growth, literally the same principles that affect differences between quartz and opal. “
Response of James Sloane to Benjamin McCann: First of all rocks do not have cells. You are confusing biology with geology.
And, yes, calcite and aragonite have different crystal structures. That was the whole point of what I was telling you. You erroneously claimed that quartz and opal are the same thing because they both contain silicon dioxide, which technically is still incorrect as silicon dioxide is a misnomer. That gets too complicated for the average person though so we will stick to silicon dioxide. Anyway, as I pointed out so many times to you, just because something has the same chemicsty, or in the case of quartz and opal, which have similar chemistry, this DOES NOT make them the same thing, Again, marble, calcite and aragonite all have the same chemistry but different crystal structures making them DIFFERENT minerals. Just like graphite and diamond are both carbon but still different minerals. Same as glucose, fructose, idose, mannose, sorbose, allose and many other sugars are C6H1206, but are all different sugars. Point is again, that simply having the same atoms in the same ratio does not make all substances with the same atoms and same ratio all the same material. Anyone with even 6th grade level of education in science should know this fact. Therefore, just because quartz is composed of silicon dioxide and opal is composed on silicon dioxide and water this DOES NOT make them the same thing as you keep erroneously stating. Again, quartz is a true solid as where opal is a solid gel. Quartz does not contain water as part of its structure as where opal does. Quartz is macrocrystalline as where opal is amorphous. Quartz forms deep in the Earth under intense pressure and heat out of supercritical water. Opals on the other hand form at lower temperatures, at shallow depths or at the surface in much shorter periods of time than it takes for opal to form. So once again you are wrong, quartz and opal ARE NOT the same thing,
Response of Benjamin McCann to James Sloane: “Let’s do some basic chemistry.
Silca: SiO2”
Response of James Sloane to Benjamin McCann: Again, not quite true, but we do not need another debate right now when I am still disproving your claims in this debate.
Response of Benjamin McCann to James Sloane: “Opal: SiO2 • nH2O.”
Response of James Sloane to Benjamin McCann: Very good. Now what is the formula for quartz? Is it identical to opal that you claim is the same thing? I will you save you the time and having to type two letters. The answer is NO!!!
Response of Benjamin McCann to James Sloane: “Opal + pressure/heat/time: SiO2 + nH20”
Response of James Sloane to Benjamin McCann: What? Now you are saying opal forms opal? Opal, which as you pointed out is SiO2 + nH20 with pressure, heat and time forms opal? No, opal again forms under low pressure, low temperatures and actually takes very little time. As the opal loses water below a 3% concentration, then the opal goes from an amorphous structure to a crystalline structure as it converts in to chalcedonies.
Response of Benjamin McCann to James Sloane: “Aluminum oxide is not part of the structure, it’s trace minerals caught in the lattice, which has the space exactly because of the extra H2O. “
Response of James Sloane to Benjamin McCann: First of all, I never said part of the structure. Although, your argument can be easily debated.
I will start with the fact that the silicic acid does not simply spontaneously form in to a gel. It requires a nucleator, which can be a variety of things such as uranium, barium, aluminum, etc. The nucleator is the basis for the “scaffolding” and this is linked to the silicic acid molecules. Thus, they ARE part of the lattice structure.
Secondly, you claim that the aluminum oxide is a trace mineral caught in the lattice for which again you provide no evidence. As pointed out, the aluminum can be a nucleator and thus part of the structure and not simply “caught in the lattice” as you claim, and the level of aluminum oxide that may or may not be present varies a lot in opals. This means it may not be present at all if the silicic acid was derived from a silica source without aluminum oxide, or the opal may have trace or higher levels of aluminum depending on the aluminum content of the silica source for the silicic acid. This is one of the factors that affects the varying density of opals, and is a factor that determines the variability in opal hardness. Higher levels of aluminum oxide in opals can increase both density and hardness. Just so you know, opals to not have a specific density or hardness. They have a narrow range of density and hardness.
Response of Benjamin McCann to James Sloane: “Opal is a mineraloid.”
Response of James Sloane to Benjamin McCann: Wow, thanks for once again repeating exactly what I already explained to you about opal being a mineraloid instead of a mineral.
Response of Benjamin McCann to James Sloane: “It’s not the end product.”
Response of James Sloane to Benjamin McCann: Again, thank you for once again repeating exactly what I already explained to you multiple times. Although, you really do not need to keep repeating exactly what I already educated you on. I already know this stuff extremely well, and my memory for this stuff is great. Therefore, you really do not need to keep telling me what I just got done teaching you.
Response of Benjamin McCann to James Sloane: “It will dehydrate until what is left is silica. “
Response of James Sloane to Benjamin McCann: Yes, again just as I already explained to you multiple times!!! The opal dehydrates in to the silica known as chalcedonies, which is a cryptocrystalline to microcrystalline quartz unlike the amorphous and water containing opal.
Response of Benjamin McCann to James Sloane: “So enjoy arguing chemistry and how they are different and not the same when they both exist in a triple point graph of SiO2”
Response of James Sloane to Benjamin McCann: I cannot believe you still do not get such as super simple fact of science. Simply having the same atoms, which opal and quartz DO NOT, does not make different things the same. I have explained this to you so many times and cannot simplify these facts any more than I have.
Response of Benjamin McCann to James Sloane: “You don’t need just depth or temperature, you need the combination”
Response of James Sloane to Benjamin McCann: Thank you for once again repeating exactly what I already just got done educating you about. I pointed out the fact the supercritical water needed to form quartz, but not opal, which is not the same as quartz as you keep incorrectly claiming, requires sufficient pressure AND temperature. Again, you really do not have to keep repeating everything I have already educated you on.
Response of Benjamin McCann to James Sloane: “that creates the pressure for supercritical fluids, which can occur way more shallow than you seem to believe. “
Response of James Sloane to Benjamin McCann: I am going to make this really easy. Show everyone here scientific evidence that supercritical fluids form NATURALLY at the surface or within 40 feet of the surface of the Earth as this is the range in which opals, which is the topic, not quartz that is something different, is formed. This ought to be fun, although I suspect you will realize your mistake I am calling you on, and you will avoid trying to provide the non-existent evidence to your claim.
Response of Benjamin McCann to James Sloane: “Your whole point has been how all chalcedony comes from opal. Flat out not true”
Response of James Sloane to Benjamin McCann: This coming from the guy who also claims opal and quartz are the same thing, which is not true. And that thinks opal converts in to opal. And who also erroneously refers to silica as a “fluid”. And that wrote “Opal is hydrated amorphous quartz”. Quartz is crystalline, the OPPOSITE of amorphous. So, opal cannot be crystalline like quartz if is amorphous. Therefore, they ARE NOT the same thing as I explained over and over to you. On top of that, even you wrote “all opal converts to chalcedony” AFTER I had already explained this fact to you. Of course, you also kept writing that chalcedony was only microcrystalline quartz until I corrected you a couple of times that it can be cryptocrystalline to microcrystalline, at which point you once again changed your wording without ever admitting to the fact you were wrong again. Therefore, right now you have very little credibility. You have your chance though to redeem yourself. Simply show everyone here the scientific proof of supercritical water formation naturally at surface level to 40 feet deep in the range of opal formation, unless you were just making crap up again.
Response of Benjamin McCann to James Sloane: “I’d never pay $1000 a carat for any form of carbon because yes they are all the same after you treat them with heat and pressure. I’ll happily take the 1/3 cost lab grown with less inclusions that DIDN’T come from a blood mine. Because chemically a diamond from the earth is the same as one from the lab.”
Response of James Sloane to Benjamin McCann: So, you would be willing to pay roughly $333 per carat for a piece of carbon when you can get a bag full of charcoal briquettes for around $10 that is also carbon? Seems pretty silly to me since you think having the same chemistry makes something the same thing. If you have a significant other, try giving them a ring with a mounted charcoal briquette and see if they agree with you that same chemistry makes that charcoal briquette the same as diamond. Then maybe you will finally understand my point, and why you are again wrong.
And if lab grown diamonds are exactly the same as naturally mined diamonds, then why are lab grown diamonds well known for reacting stronger to fluorescent lighting and fluoresce longer than naturally mined diamonds? If they are exactly the same, then they should react exactly the same. By the way, one of my projects I am working on is low pressure diamond synthesis, so I am well versed on diamonds and their structures and formation as well. So, if you wish to debate diamonds after I finish educating you on opals, we can start a new thread.
By the way, not all mined diamonds are blood diamonds. Diamonds are found in various places around the world and are even mined here in the United States and in Canada. So, you really think those are blood diamonds?
You keep making these false accusations that I am wrong then repeat what I already educated you on as fact. Now you are claiming that the studies I am posting do not support my position, which is also false. This is why you cannot provide any evidence to the contrary including you cannot quote anything in these abstracts that prove my claims wrong because as usual, you are just making crap up to try and save face after being totally discredited.
Response of James Sloane to Benjamin McCann: Since Benjamin McCann still does not understand the geology of chalcedony formation, I have yet another study for him. Prior study I posted already went to in to biogenic silica in ocean water forming opal then converting in to the chalcedony chert/flint. What is the other major chalcedony? Agate. So, let's take a look at agate formation. www.researchgate.net/publication/233648978_The_formation_of_agate_structures_Models_for_silica_transport_agate_layer_accretion_and_for_flow_patterns_and_flow_regimes_in_infiltration_channels The silica gel being referred to has to convert in to opal before it can convert in to chalcedony. This is why I keep asking Benjamin McCann to explain how chalcedonies supposedly spontaneously form from silica as he implies, which he keeps evading because that is not how things work. The recycled solvent in the gel referred to in the study is water. Again, as water is lost from the silica solution a gel is formed first. As the water content drops below 24%, the result is opal formation, which again is a solid silica gel with amorphous structure. When enough water is finally lost from the opal gel (below 3%), the opal then starts to crystallize in to a layer of chalcedony. As this process keeps repeating, alternating colored bands of chalcedony form resulting in agate formation.
I learnt a new skill for debating. 
Maybe you can post some pictures here