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Post by Jugglerguy on Jan 10, 2021 12:24:31 GMT -5
I probably would have just called those quartz, but they do look more transparent than most quartz that I find. Of course agate is quartz, but you know what I mean. Rocks sometimes look way more interesting when you take a picture and enlarge it because it shows so much more detail. I might need to look closer at some of the quartz I have picked up. I’m not sure if I have any like that or not.
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Post by holajonathan on Jan 10, 2021 13:25:00 GMT -5
I probably would have just called those quartz, but they do look more transparent than most quartz that I find. Of course agate is quartz, but you know what I mean. Rocks sometimes look way more interesting when you take a picture and enlarge it because it shows so much more detail. I might need to look closer at some of the quartz I have picked up. I’m not sure if I have any like that or not. One of your Youtube videos of boxes of Lake Superior rocks has a rock (somewhere in the 2:00-3:00 section, I think) that looks related. I will try to find the video. I think you classified it a "magate" because it had agate-like qualities but not traditional agate-like concentric banding. Of course, not all agates have banding... I have thought that a number of your "magates" were in fact agates. Here is why I think the ones I am finding are agate. I could be wrong. 1. The surfaces have a waxy luster and what appears to be the imprint from the rock that once encased them. These irregularities are superficial and wear away, as they do with agates. 2. They crack like agate and not like quartz. Quartz cracks are more visible and often look white; Agate cracks are finer and cleaner. I assume that crystal size accounts for this. 3. They polish better (shinier) than quartz. The oolitic areas sometimes undercut a little, but most areas get the glass-like agate shine. 4. The color palette and patterns are unlike quartz I have seen. 5. They seem heavier than quartz. I will try to calculate their density and compare to quartz and known agates. 6. They resemble Moroccan Berber oolitic agate in terms of color palette, color patterns, and structure. I just bought some Berber oolitic agate rough from Ebay to tumble and compare since that seems to he the most commonly-recognized oolitic agate. If you get a chance, look very closely at some of your Lake Superior "magates" and I think you will find one or more related specimen. |
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Post by holajonathan on Jan 10, 2021 13:57:25 GMT -5
 This is the one I had in mind. Not quite as similar as I had remembered, but somewhat similar. |
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Post by Jugglerguy on Jan 10, 2021 20:46:00 GMT -5
That's a really good example of what I was thinking about. I don't think that's an agate, but I could be wrong. Agates break with a conchoidal fracture. Regular quartz does not. I'm not sure if cracks differ. I also didn't realize that agate is more dense than quartz since it is quartz. You should post your pictures on the Lake Superior Agate Collectors group on Facebook. There are some experts there who might be able to identify your rocks. On the other hand, they might just tell you that they're not Lakers, but they could still be some other sort of agate.
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Post by holajonathan on Jan 11, 2021 3:25:05 GMT -5
That's a really good example of what I was thinking about. I don't think that's an agate, but I could be wrong. Agates break with a conchoidal fracture. Regular quartz does not. I'm not sure if cracks differ. I also didn't realize that agate is more dense than quartz since it is quartz. You should post your pictures on the Lake Superior Agate Collectors group on Facebook. There are some experts there who might be able to identify your rocks. On the other hand, they might just tell you that they're not Lakers, but they could still be some other sort of agate. Good idea. I will post to the facebook page when I get a chance. I have some small pieces that will not tumble well. When I get a chance I will hit them with a hammer. I am familiar with how agates fracture... sort of like glass. My current thinking is that the rocks I have are sedimentary rocks with some agate and some quartz in them. From what I have been reading, agates can form in sedimentary rocks, although they form much more commonly in volcanic rocks. Volcanic rocks are a better host for agate formation because the volcanic rocks leach a lot of dissolved silica, which is what is needed (in super-saturated concentrations) to form agates. (I assume the silica becomes super-saturated when it is first dissolved to 100% saturation in hot water, and when the water cools, its capacity to hold dissolved silica decreases, thus super-saturating the dissolved silica. My assumption is based on what I recall of high school chemistry class 22 years ago). Sedimentary rocks do not necessarily leach dissolved silica, or if they do, it is less likely to be in concentrations sufficient to form agate. To form agate, the water entering and exiting the void has to be super-saturated with silica. Super-saturated silica creates a gel of dissolved silica that sticks to the inside walls of the void, and later hardens into agate. If the water is high in dissolved silica, but not super-saturated, quartz crystals form instead of agate. This is why many agates have quartz in the center: as the agate layer got thicker and thicker, less silica-rich water could make it into the center of the nodule, and there was merely enough silica present to form quartz, but not agate. This also explains why quartz is the most common form of crystalline silica in sedimentary rocks like limestone and dolomite, and agate / jasper / chert / flint are the most common forms in volcanic rocks. The silica leaching from the volcanic rocks was the key. The preceding two paragraphs is merely my lay understanding after a few hours of reading. Maybe you could ask your son-in-law about this? Finally, quartz and agate are both crystalline silica, but since the crystal structure is different, I don't think they necessarily have the same density. Graphite and diamonds are both crystalline forms of carbon, but diamonds have a density of 3.5 g/cm3 whereas graphite has a density of around 2.1 g/cm3. It seems like with the Lake Superior agates I have bought, the ones that ended up having a ton of quartz inside were a lot lighter than the ones that had little or no quartz. The difference in weight seemed so obvious that I never thought about it seriously -- it seemed obvious. But your point is a good one. Something else to ask your son-in-law? |
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2raise4boys
off to a rocking start
Member since September 2023
Posts: 1
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Post by 2raise4boys on Sept 20, 2023 21:28:29 GMT -5
What an enjoyable read! I love love love the green rock!! Wowee!
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