Reply To: What minerals form the brachiopod geode crystals?

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#16832
Jack Kallmeyer
Moderator

@matteo-di-angelo @lcone   Matt, your chemical tests are spot on for Dolomite.  In the cases here (Lee’s samples and mine) the crystal shape is the dead giveaway.  These crystals exhibit a form not seen in Calcites.  They are very thin curved rectangular shapes – kind of like a potato chip that is rectangular rather than oval.  The crystals lining the brach have been shown to be Calcite by tests like yours.  I attached a cropped photo of the one I sent earlier to show (hopefully) the curved crystal shape of the Dolomite.

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