New Idria Mine (New Idria group; New Hope vein), Idria, New Idria District, Diablo Range, San Benito Co., California, USA
Cabinet, 11.8 x 5.5 x 4.6 cm
A large, pretty specimen of fibrous, stark white artinite (Hydrated Magnesium Carbonate Hydroxide), from California. It forms as a crust of acicular to fibrous crystal aggregates sometimes collected into tight perfectly spherical balls (as here). People are usually surprised when told that it is a carbonate, because it has the appearance of several silicate minerals and forms in a somewhat atypical carbonate environment.