CONNOISSEUR'S CHOICE Distinctive Twinned Calcite from the Palmarejo Mine, Chihuahua, Mexico

摘要

Calcite comes from such a seemingly infinite number of worldwide localities and shows such a bewilder-ingly wide range of colors and associations, forms, and habits, including twins, that new finds struggle to catch the attention of collectors who are already drowning in specimens of this supremely common and supremely beautiful mineral. Thus it is significant that a recent and notable occurrence of distinctive calcite specimens from the Palmarejo mine in western Chihuahua, Mexico, has joined the short list of exceptional localities. These immediately recognizable specimens include individuals and groups of up to twenty elongate twinned crystals to 25 cm in length. The best of these specimens are partially encrusted with white palygor-skite (powder XRD and EDS identification: J. E. Post) that is rimmed by a thin layer of black manganese oxide-included calcite (principally romanechite and chalcophanite; J. E. Post) that is itself encrusted by a later stage, or stages, of calcite crystals that create a beige-to-colorless fringe outlining the earlier white-coated twins.