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Identity HelpAny ideas about the brownish crystals?

21st Sep 2019 21:50 BSTali heral

This stone comes frfom Aydıncık- Yozgat - Turkey. Its found in an area where dominant rocks are andesite. Lots of quartz and amethyst around. Have not done hardness or SG tests since this is the only sample I have and dont want to ruin it. No reaction to acid. Wondering about the big brownish crystals over quartz. Any lead will be appreciated.

21st Sep 2019 21:52 BSTali heral

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photos 1

22nd Sep 2019 15:37 BSTThomas Lühr Expert

0205747001375191855.jpg
Siderite? 

22nd Sep 2019 11:09 BSTNoah Lunster

I think this is Calcite on Quarz.

22nd Sep 2019 13:30 BSTKevin Conroy Expert

Which acid was used for the test?  Muriatic (hydrochloric) acid or vinegar should cause bubbles to form from the brown crystals if they are calcite (which is also my first thought).

22nd Sep 2019 17:41 BSTDonald B Peck Expert

Crystallography is trigonal (views down the c-axis show it to be a 3-fold axis of rotational symmetry) . . . I think it is either calcite or siderite,  since it didn't bubble with acid, probably siderite.

22nd Sep 2019 20:05 BSTEd Clopton Expert

Check for fluorescence under SW UV.  If it fluoresces, it's definitely not siderite (the iron in the siderite would quench any fluorescence) and probably is calcite.  If it doesn't fluoresce, then either one is still possible. 

22nd Sep 2019 20:31 BSTPaul Brandes Manager

I believe this be calcite on quartz as well, but as Kevin mentioned, did you use the correct acid, Ali? Also, did you test the brown crystals or the quartz under it (which would not have reacted to acid)?

22nd Sep 2019 21:14 BSTali heral

Thank you very much for your comments. I will repeat the acid test tomorrow. Majority says its calcite.
 
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