Twinned Calcite "Black Diamond" cleavage (RARE old CA)

Item Description

A surreal, VERY RARE old calcite cleavage from the Mojave Desert. This is a fantastic two-sided cleavage of a large included calcite twin. The proposed process of formation is a three-phase sequence: 1.) Initial crystallization of scalenohedral calcite crystal containing lead and manganese activators, resulting in bright orange/red fluorescence; 2.) Deposition of non-fluorescent manganese oxide coatings on crystal surfaced, resulting in dark cross-sectional outline; and 3.) Formation of additional twinned calcite, not containing lead and manganese activators, that encased the original fluorescent calcite scalenohedron within a larger mass of colorless and weakly-fluorescent calcite. When the resulting formation is cleaved, a diamond-shaped cross section of the original fluorescent calcite crystal is revealed within a larger colorless twinned groundmass. (Robbins, Fluorescence, Gems and Minerals Under Ultraviolet Light, 1994). These were also known as "Black Diamonds". Ex J.G Dixon and Tom Wolfe Collections. It comes with a The Bradleys label dating from 1950 to 1958 and the specimen was given to J.G Dixon by them. Unique, amazingly exotic old calcite from an obscure locale. A MUST for the species, fluorescent or California collector!