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Search found 15 matches |
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Dean Allum Replies: 21 Views: 16325 |
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Pete,
After reading this article, I have another theory for you to consider. Epitaxial marcasite on pyrite from Rensselaer, Indiana -K. J. Brock; L. D. Slater American Mineralogist (1978) 63 (1-2 ... |
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Dean Allum Replies: 21 Views: 16325 |
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Pete,
Thank you for posting this fun puzzle for us to think about over the holidays. 1) I own many spherical pyrite concretions formed in a limestone environment, nucleating on organic matter. Is ... |
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Dean Allum Replies: 65 Views: 173317 |
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Fred, Jordi, Roger,
All these photographs are magnificent by themselves. The fact that they were taken through glass, and the reflections are negligible makes them miraculous. Thank you. -Dean |
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Dean Allum Replies: 157 Views: 284779 |
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James,
Nice post! That hole appears to be a flat spot in a concave recess. Do you know that it extends all the way through the specimen? Pete, A cyclic twin with a hole in the center (similar to ... |
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Dean Allum Replies: 13 Views: 31374 |
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These "A-type" muscovite books are common in Fremont and Park county pegmatites in Colorado. Several local collectors think these are a type of twin, but now I am not sure. Notice that the A ... | |
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Dean Allum Replies: 157 Views: 284779 |
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Wow, I was just about post a question about the atomic origins of crystal twinning.
Elise, Do you have a pdf copy of that nanoLetters paper? Regards, Dean ALlum |
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Dean Allum Replies: 157 Views: 284779 |
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Pete,
Your competing poly-crystals theory for cyclic twinning is elegant! Wouldn't there be some remaining evidence of the nucleation site at the central vertex which you could view with a TEM of ... |
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Dean Allum Replies: 157 Views: 284779 |
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Pete,
Your competing poly-crystals theory for cyclic twinning is elegant! Wouldn't there be some remaining evidence of the nucleation site at the central vertex which you could view with a TEM of ... |
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Dean Allum Replies: 19 Views: 72114 |
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I can't believe there were no pictures of perhaps the second best mineral exhibit of all time!
Collections manager, Ed Raines, has put together a showcase of Colorado Rare Earth minerals. This Glor ... |
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Dean Allum Replies: 21 Views: 45436 |
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David,
Let's try out some of the responses to real world "Great Collectors". Here is a short list of legendary collectors which most people would classify as "great". James Sm ... |
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Dean Allum Replies: 14 Views: 20639 |
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The concept of running out of mineral specimens is so foreign to me.
I regularly visit old mine sites in the Rocky Mountains having abundant dumps. They appear to have not been visited for decades ... |
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Dean Allum Replies: 122 Views: 189820 |
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Gail,
Now that you and Jim are in the market for a set of bowling pins, have you seen this? https://www.mindat.org/photo-58452.html -Dean Allum |
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Dean Allum Replies: 14 Views: 21763 |
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Phil,
Exactly which legislative initiative in Arizona are you talking about? Then, what do you believe is the motivation of Arizonans for passing this legislation? -Dean |
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Dean Allum Replies: 7 Views: 14813 |
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amethystguy,
I usually go for quantity over perceived quality. The rocks that we typically deal with are unusual in nature. It is more unusual to have a large rock than a perfectly formed microscopic ... |
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Dean Allum Replies: 16 Views: 25448 |
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Duncan,
I created that setup and saw 4-extinctions per 360 degree rotation when the Z-axis was perpendicular to the light. This setup does not appear to work if the surface is frosted or there are ... |
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