2.9" Marcasite Included Calcite Crystals with Dolomite - New York

This is a beautiful, 2.9" wide specimen featuring calcite crystals with need-like marcasite inclusions, formed from a dolomite crystal encrusted matrix. It comes out of the Benchmark Quarry in Montgomery County, New York, one of several sites known to produce "Herkimer diamonds".

Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.

Marcasite, Calcite & Dolomite
Benchmark Quarry, St Johnsville, Montgomery County, New York
Specimen: 2.9 x 2"