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Identity HelpCalcite and ? in vug from Ohio
3rd Mar 2012 05:55 UTCJamie Cheshire
The host rock seems to be an iron oxide-cemented siltstone with calcite crinoid stem parts. There are many small vugs with calcite crystals throughout. The pictures are a single vug split in half; field of view is about 14 mm. What are the needle-like crystals? Some are kind of cylindrical, but others are flat. The white angular material is probably calcite (I put 5% HCl on some scrappier examples and got fizz).
Thanks,
James
3rd Mar 2012 10:24 UTCDana Slaughter 🌟 Expert
They look like gypsum crystals to me. Nice find!
Dana
3rd Mar 2012 10:36 UTCBob Harman
3rd Mar 2012 12:36 UTCChris Stefano Expert
3rd Mar 2012 17:41 UTCUwe Kolitsch Manager
3rd Mar 2012 18:26 UTCJamie Cheshire
4th Mar 2012 17:19 UTCsteven garza
I agree they are probably aragonite, &, darned nice ones, also. I also think (for experience's sake, if nothing else) you should perform the acid test Bob suggested, EXCEPT, instead of putting the acid on the xls (crystals), you should take a small needle, to pry off a single xl, near the outter edge of the specimen (I see several candidates for this) & test THAT, by dropping it into a drop of acid on glass. It should give very satisfactory results, without damaging your other xls.
Since calcite & aragonite have the same composition (they are called polymorphs, which means it has several forms/minerals with the same composition; graphite & diamonds are a good example of this situation), that means that many locations that have calcite xls, can be expected to also have aragonite, in one form or another. This is especially true in sedimentary deposites.
Your friend, Steve
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