2.1" Gemmy Dioptase and Mimetite on Dolomite - N'tola Mine, Congo

Gemmy Dioptase and Mimetite on Dolomite - N'tola Mine, Congo #209337

This is a very nice association of dioptase crystals and mimetite from the N'tola Mine of the Republic of the Congo. The entire specimen is 2.1" wide. The dioptase crystals have a saturated, dark emerald-green color while the mimetite is vibrant orange in color and is primarily found along what could be considered the back side of the specimen. The mimetite and dioptase crystals formed from a dolomite encrusted matrix.

Dioptase is an uncommon mineral, found mostly in desert regions where it forms as a secondary mineral in the oxidized zone of copper sulfide mineral deposits. This copper-based mineral forms small rhombohedral crystals, typically less than 0.75 centimeters in length. It is popular with mineral collectors due to its vibrant color and it is occasionally cut into small emerald-like gems.

Mimetite is a lead chloro-arsenate mineral with the chemical formula of Pb5(AsO4)3Cl. Depending on conditions during formation/replacement, arsenate radicals (As04) can be replaced by a phosphate (PO4) or vanadate (VO4) radical. This alteration is what leads to the formation of pyromorphite and vanadinite, hence why they are typically found associated with each other. Often red to yellow in color, mimetite can occur in a variety of structures, from small prismatic clusters and crusts to incredible hexagonal crystals both thick and thin.

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