Dolomitic marble is a crystalline-textured, ~monomineralic metamorphic rock. It is composed of dolomite (CaMg(CO3)2). Dolomitic marbles form by metamorphism of dolostones. These rocks are identified by effervescing (bubbling) in acid when powdered. Some dolomitic marbles have a noticeable tremolite component (Ca2Mg5Si8O22(OH)2).
Dolomitic marble (10.3 cm across) - glacial clast derived from Upper Pleistocene till in Granville, Ohio, USA. Specimen found & owned by Ryan Martyn.
Stromatolitic metadolostone (15.2 cm across) from the Kona Dolomite (Paleoproterozoic, ~2.20-2.29 b.y.) of the Marquette area, Upper Peninsula (UP) of Michigan, USA. Some metamorphosed dolostones are referred to as metadolostones. This one, from the Precambrian of northern Michigan, was originally a dolostone having stromatolitic laminations. Stromatolites are large, layered structures built up by mats of photosynthetic cyanobacteria in very shallow water facies.
Specimen owned by Tabatha Beaver & Matthew Hartman.