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Calcite after Aragonite - Sold

Calcite and aragonite share the same chemical composition, calcium carbonate. At the surface of the earth, the calcite crystal structure is more stable than that of aragonite, but certain biogeochemical processes and physical conditions do favor aragonite formation.

The Cadman quarry, also known as the Monroe quarry, has been producing calcite specimens since the 1970s, judging by its mention in Cannon's 1976 Minerals of Washington. This is interesting pseudomorph, wherein small calcite crystals (2-4 mm) have replaced prismatic aragonite crystals. These specimens are rarer than the colorless discoidal calcite crystals also known from this locality. Some Washington collectors slice these pseudomorphs, revealing some interesting internal zoning. The prismatic habit shows fishtail twinning, like gem aragonite twin crystals from Číčov, Czechia. This specimen is essentially a prismatic single crystal. At the base of the crystal some attachment points are present. Nice.