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Post by jakesrocks on Jun 23, 2012 20:27:31 GMT -5
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Post by Pat on Jun 23, 2012 20:48:47 GMT -5
RocknCritter, glad you corrected that. Didn't think meteorites were glass. Jake, thanks the the photo.
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Post by 3rdrockfromthefun on Jun 23, 2012 22:16:39 GMT -5
Frank, why do you think it is glass? I don't care which it is, but I do want to know how to tell the difference. you will NEVER find obsidian in clear colors like that purple or some of the clear grass to dark green, or bright clear yellows they pass off as obsidian the man made glass colors just don't exist in the obsidians, if you ever go and find any out rock hunting let us know because it will be very rare! I see what you're saying and I'd agree at least as much as in saying that I sure haven't seen anything like that. The bright colors of obsidian are usually 'reflective', not 'refractive', so looking through any brightly colored sheen will most likely not yield the same translucent color. Obsidian seems to be generally softer than most common glass. It even has a different sound when two pieced are tapped together - a dull clack rather than a clink. I have seen optical glass as soft and perhaps even softer (lenses - many of which can be scratched by the impurities in a cotton swab). Anyway... given the variables that can occur in nature and the number of surprises I've had myself with obsidian - I'm wondering if there is no concrete method of verifying something is NOT obsidian other than experience. Don't know... |
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Post by FrogAndBearCreations on Jun 23, 2012 22:24:46 GMT -5
Moldavite is considered to be a re-entry glass as its from the meteor strike that blew it off the face of the earth and it came back down as what you see, it is very high in silica - its a tektite not a meteor
its one of the beautiful tektites
a lot of them are black or brownish
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Post by Pat on Jun 23, 2012 22:57:21 GMT -5
I appreciate the discussion, and I'm learning something about glass and a few other things.
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Post by jakesrocks on Jun 23, 2012 23:03:37 GMT -5
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Post by FrogAndBearCreations on Jun 23, 2012 23:10:26 GMT -5
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Post by helens on Jun 23, 2012 23:46:24 GMT -5
RocknCritter, glad you corrected that. Didn't think meteorites were glass. Jake, thanks the the photo. Meteorites ARE glass, or at least are made of the same components (primarily silica with an amorphous crystalline pattern - aka no specific crystal pattern). They are natural glass vs man-made glass, but they are still considered glass. Glass itself probably came about from someone finding a patch of sand (silica) that got hit by lightning and someone said... OHHH... you heat sand enough... you can SHAPE it!! Somewhat maybe like people figured out that if you heat iron ore (rocks), you can get the iron out and shape it. I called it 'meteorite' because it includes moldavite AND tektites. But this is why there is such controversy about the authenticity of moldavites and tektites on the market. There appears to be far more of it sold than can exist in nature. It can take 15 seconds to 'make' a piece of either from green or black glass if you have those colors. And you can ALWAYS make glass opaque or swirly, or add bubbles in patterns, and press or manipulate the surface to get the right texture. Here is gemology online's definition for moldavite: www.gemologyonline.com/moldavite.html"Moldavite is a naturally occurring glass, originally found along the Moldau River in Czechoslovakia in 1787. It is usually a dark olive green color but can also occur in muted yellows and browns. It is one of a handfull of gems that can claim an extraterrestrial origin*. Moldavite is believed to be the outer surface of meteorites, that fused and melted during entry into our atmosphere. Moldavite has a diagnostic pattern of striae and bubbles (elongated, torpedo-shaped) that are unlike man-made glass. It does not contain crystals like those found in volcanic glass or obsidian. The Holy Grail is said to be carved out of a green stone that fell from Satan's crown as he descended from Heaven to Hell. Popular legend has long claimed this stone to be an emerald. It has recently been proposed that the Holy Grail may have been carved from moldavite, using the stone falling from Satan's crown as a metaphor for the green stone falling from the sky." Glass can be shaped, molded, worked into practically any shape/texture/color/pattern. The thing is, it can be very time-consuming to work, so BUYING natural glass already patterned is often easier and far cheaper than working glass. But something like moldavite and tektite are so easily and cheaply copied that it's being done all over the place. Google 'fake moldavite' or 'fake tektites', you get a HUGE number of articles. |
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Post by helens on Jun 24, 2012 0:15:53 GMT -5
you will NEVER find obsidian in clear colors like that purple or some of the clear grass to dark green, or bright clear yellows they pass off as obsidian the man made glass colors just don't exist in the obsidians, if you ever go and find any out rock hunting let us know because it will be very rare! I see what you're saying and I'd agree at least as much as in saying that I sure haven't seen anything like that. The bright colors of obsidian are usually 'reflective', not 'refractive', so looking through any brightly colored sheen will most likely not yield the same translucent color. Obsidian seems to be generally softer than most common glass. It even has a different sound when two pieced are tapped together - a dull clack rather than a clink. I have seen optical glass as soft and perhaps even softer (lenses - many of which can be scratched by the impurities in a cotton swab). Anyway... given the variables that can occur in nature and the number of surprises I've had myself with obsidian - I'm wondering if there is no concrete method of verifying something is NOT obsidian other than experience. Don't know... I agree with everything you said, but wanted to add that glass can be made in so many different formulas that affect both hardness and COE (coefficiency of expansion- how much it shrinks and expands when heated), that I don't think it's possible to give a 'rule of thumb' for hardness compared to obsidian. Both have different mineral contents depending on many factors... in the case of glass, what you add to it to get the color for example. You can REALLY tell when you heat it and play with it how much hardness can vary, especially when molten. I don't have a ton of experience with obsidian, but the few I've ground haven't seemed much harder/softer than the bit of glass I've ground (not much of either, I'm very new to cabbing), but I'm sure that highly colored obsidians would be softer than say clear borosilicate glass, because those colors come from other minerals:). BUT!! You ABSOLUTELY can make any obsidian colors your heart desires in glass... but the cost in trial and error for glass blending to catch 1 color variation/pattern/texture would be so outrageously costly and time consuming that no glass worker in their right mind would attempt it. If obsidian ever cost more than $100 a lb tho, you betcha they'd be cranking out obsidian in China for sale on ebay like they do meteorites today (tektites and moldavites). Glass imitation opals (Gilson opals) cost MORE than real opals except the best gem grades. Anything that is roughly the same coe of 4.5-5.5 can be suspected to be glass if the original is more expensive than the cost of making it in glass. I want to mention something I said earlier that wasn't quite accurate... slag/cullet glass is WAYYYY cheaper than glass working rods/sheets/stringers, because it's the waste, the bottom of the barrel so to speak, during glass manufacturing, where reproduce-able precise color is the goal. But you can get some gorgeous oddities and colors out of slag sometimes because of that incomplete mixing. So it's not technically true that glass is more expensive than obsidian rough if you are talking about slag/cullets... on the other hand, I would imagine you could get the same price or more for a glass cab as you could for an obsidian cab of roughly the same colors/size/cut. Drinking glassware is very very cheap... art glass can be as expensive as precious gems. Here's a gallery with some contemporary artist pieces that have really lovely photos. I am far too lazy to spend weeks working on individual pieces except for contests, so I don't go for the larger picky galleries with my work, I prefer small museums that don't pressure me to create constantly. But to put in perspective why glass can costs so much, check Pismo out: www.pismoglass.com/searchresults.php?artistId=10041043&start=1&showtitle=&cat=o |
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Post by 3rdrockfromthefun on Jun 24, 2012 6:33:21 GMT -5
Pretty impressive glassworks. I'll stick with stone - it's complex enough  I notice whenever I research obsidian that there is a lot of mis-information out there and a lot of conflicting information. I have seen it called crystalline (wrong - it's amorphous) and read of sheen colors being created from everything from iridescence from tiny gas bubbles to impurities (my opinion is that it is more likely both or just impurities) |
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Post by jakesrocks on Jun 24, 2012 6:38:36 GMT -5
Helen, I care to differ with you on your first statement. "Meteorites ARE glass, or at least are made of the same components (primarily silica with an amorphous crystalline pattern". I have a total of 19 small meteorites in my collection, and I can assure you that not one of them is comprised of glass. I also have a tectite and 2 pieces of moldavite which are a form of glass. There are dozens of classifications of meteorites, and only a very small portion of them contain any silica at all. Here's a very quick reference to the types of meteorites. There are 3 basic classes of meteorites, which are broken down into dozens of sub- classifications. www.meteoritemarket.com/type.htm |
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Post by johnjsgems on Jun 24, 2012 8:23:11 GMT -5
Obsidian is volcanic glass. Many similarities to man made glass. Your picture looks like glass glass to me. Some of the slag glass has unbelievable colors that give it away.
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Post by Pat on Jun 24, 2012 13:04:10 GMT -5
Question: Are there significant differences between manmade glass and obsidian found with official rock testing equipment? Do the ingredients/components of both glass and obsidian fall within the same range? Thanks.
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Post by jakesrocks on Jun 24, 2012 13:31:50 GMT -5
The chemical formula for obsidian is SiO2, plus MgO, Fe3O4
Common man made silicate glass. Na2K2Si4 alkaline silicate glass.
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Post by Pat on Jun 24, 2012 13:37:23 GMT -5
Jake, looks like obsidian is basic glass +. Is the + significant for ID purposes? Is there any obsidian that is just SiO2? (I hope not!)
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Post by jakesrocks on Jun 24, 2012 13:43:02 GMT -5
If obsidian were just SiO2, it would be water clear and colorless. It's other mineral impurities which give it various colors. Same holds true for man made glass.
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Post by helens on Jun 24, 2012 13:46:08 GMT -5
Helen, I care to differ with you on your first statement. "Meteorites ARE glass, or at least are made of the same components (primarily silica with an amorphous crystalline pattern". I have a total of 19 small meteorites in my collection, and I can assure you that not one of them is comprised of glass. I also have a tectite and 2 pieces of moldavite which are a form of glass. There are dozens of classifications of meteorites, and only a very small portion of them contain any silica at all. Here's a very quick reference to the types of meteorites. There are 3 basic classes of meteorites, which are broken down into dozens of sub- classifications. www.meteoritemarket.com/type.htmI see. And after you said that, I realized that I've seen and touched a moon rock at the Kennedy Space Center and it's clearly not glass either. Nearly everything I've read about meteors associate them with glass. And of course, since tektites and moldavites are glass, it was a lazy assumption that all meteorites are glass, which I already knew for years was not from the moon rock. From National Geographic: news.nationalgeographic.com/news/2006/12/061221-egypt-glass.htmlEvery time an article talks about meteors, glass is mentioned, ie., from Geology.com: geology.com/meteorites/impactites.shtmlThe interesting part is that the more I read about it, the more I'm wondering if meteorites are EVER glass, it seems that glass is found more from point of impact than from the meteor itself, and there is no concensus whether any glass is extraterrestial. From wiki: en.wikipedia.org/wiki/Tektite"Though the meteorite impact theory of tektite formation is widely accepted, minority theories propose alternate ideas of tektite formation.
Tektites contain no cosmogenic noble gases produced by cosmic rays, a factor that excludes long travel in space, necessary if tektites are not terrestrial. <...>
From the 1950s through the 1990s, NASA aerodynamicist Dean R. Chapman and others advanced the "lunar origin" theory of tektites. Chapman used complex orbital computer models and extensive wind tunnel tests to support the theory that the so-called Australasian tektites originated from the Rosse ejecta ray of the large crater Tycho on the Moon's nearside. Until the Rosse ray is sampled, a lunar origin for these tektites cannot be ruled out. During the 1980s and 1990s, researchers such as O’Keefe of NASA, astronomer and long-time tektite researcher Hal Povenmire, and petrologist Darryl Futrell claimed that the slow way in which tektite glass formed (called "fining"), and the volcanic features they claimed to have observed within some layered tektites, could not be explained by the terrestrial-impact theory. Unlike all terrestrial impactite glasses, tektites are nearly free of internal water, similar to lunar rocks. Also, Stokes' Law does not permit the formation of tektites during impact[citation needed] while the velocity needed to form certain "flanged" tektites is more compatible with a lunar origin rather than a terrestrial origin.[citation needed] O'Keefe suggested explosive, hydrogen-driven lunar volcanoes as the original source of tektites. Interesting stuff:). |
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Post by helens on Jun 24, 2012 14:00:34 GMT -5
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Post by jakesrocks on Jun 24, 2012 14:16:06 GMT -5
Helen, tons of space glass and other space debris falls on the earth every day. Some space rocks do contain small amounts of silica. For the most part, the silica will vaporize on entry into the earths atmosphere, and falls to earth as particles no larger than talcum powder. Other minerals rain down on the earth as well in tiny particles.
So, if as these scientists say, tektites came from the moon or from deep space or whatever, what prevented them from vaporizing when they entered our atmosphere ? Remember, glass has a fairly low melting point. And what about the glass that was formed by the heat and pressure of our own nuclear tests in Nevada ? The ground around those test sites is littered with radioactive glass particles which weren't there before the tests. ( I'm working on trying to obtain a sample of that glass, which will be enclosed in a sealed leaded glass ampule.)
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Post by helens on Jun 24, 2012 14:42:48 GMT -5
Actually, glass has a high melt point AND loves to stick together. I put a few small rocks in my kiln out of curiosity and slowly brought it up, then held them at my glass annealing temps (1058 degrees F). Within 2 hours all 4 broke into pieces, 1 violently exploded (I THINK this was the agate). I fished them out before the other 3 could explode. What a mess. That experiment was a piece of flint ridge flint from Sue, yermo agate from Paul, mozarkite from builtonrocks, and a piece of limestone fossilized shells hubby found at the space center. The piece that was most intact was the mozarkite. Glass doesn't ever break from temperature like rocks do (what those rocks did surprised the heck out of me), it just melts, then resolidifies. Reentry temperature is 3000 degrees F per this: en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_systemAll that would do is melt the glass, and it would solidify as soon as reentry was complete and it cooled. There's nothing in the act of falling that would break the molten glass apart unless it hit something, OR the cooling was too sudden (glass shatters in extreme temperature differentials). If cooling is too sudden, glass would fragment (think cracking pyrex dish from putting in cold water after coming out of oven) into large chunks. The only exception to this would be tempered glass, which is designed to fragment super small. I can't imagine a multi-mineral rock holding up better than glass during reentry if it can't even stay solid in a kiln through ordinary glass annealing. That doesn't mean tektite came from the moon at all, but atmosphere entry conditions would seem to make it EASIER for glass to get through than other rock types intact. But IF it came from the moon, it leads the the question... is the moon composed of as many varied rock minerals as the earth? When you look at moon landing photos, it all looks like a pretty uniform surface. I'm really skeptical that all that white powdery dust/rocks we see in the photos of the moon surface then becomes nice bright green/yellow glass on the side of the moon we can't see. And for a fact, melted sand makes glass, since that's how glass was first made, melting beach silica (quartz), so ANY high temperature impact would make some type of glass if there's ANY quartz silica around the impact site. Around the turn of the century a super popular glass (even Tiffany used it) was called Uranium glass. They used it for all kinds of things, from art deco to the depression glass era, and I have some of the original tubes made. It's glass colored with Uranium, and you can still find it all over Ebay. You may recognize this from your mom's dishware (it glows in the dark): www.bonanza.com/listings/Antique-Art-Deco-Uranium-glass-sett-3-small-dishes-Tray/14724457Point here is... I'm not sure how well glass absorbs radioactivity... you may not need to seal it in lead. I will look into it when I get back:). |
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