DENVER SHOW: DIOPTASE BEST $2 MINERAL

On November 24 I reported on the Denver Area Mineral Dealers fall 2019 Gem and Mineral Show held at the Jefferson County Fairgrounds on November 15-17.  I picked up some nifty minerals (see the Post) but thought I ought to mention the Best $2 Mineral Added To My Collection!  In fact, I thought it was a real find—a gemmy green cluster of dioptase crystals, a hydrated copper silicate [CuSiO₃-H₂O]. 

A cluster of gemmy green dioptase crystals.  Width of specimen ~3 cm.

The crystals are vitreous, emerald green in color and have a hardness of around 5.0 (Mohs) with a green streak.  Crystals are quite brittle, easily cleave, are fragile, and usually have a conchoidal to uneven fracture when broken (not along the cleavage planes).  Crystals are translucent to transparent, belong to the Trigonal Crystal System, and generally are 6-sided (hexagonal) with a rhombohedral termination.  It appears to me that once rockhounds see the emerald green variety of dioptase crystals, the sight will appear in their mind forever! 

Dioptase crystals.  Width FOV ~1.8 cm.

Drawing of dioptase, modified rhombohedral crystal.  Courtesy of smorf.nl with original from Goldschmidt, Atlas de Krystallformen, 1913-1923.

Nice modified rhombohedral crystals of dioptase (Trigonal Crystal System).  Width FOV ~ 4 mm.

Drawing of dioptase, modified rhombohedral crystal.  Courtesy of smorf.nl with original from Goldschmidt, Atlas de Krystallformen, 1913-1923.

The “softness” of dioptase (5.0 Mohs) easily distinguishes them from hard emeralds (8.0 Mohs)—for those of you who identify minerals for treasure hunters.  In fact, in the late 1700s copper miners working at the Altyn-Tyube Mine in the Ural Mountains of Kazakhstan thought they had discovered a giant emerald deposit when suddenly beautiful green crystals started showing up.  I presume many of the green crystals were taken out via lunch bucket by the Russian and Kazakh miners before the mineralogists/chemists working in Moscow said, “sorry boys, too soft for emeralds.”  Even today the Altyn-Tyube in the premier collecting locality for dioptase and the source of my specimen.  

  

Dioptase forms in the oxidized zone as a secondary mineral where copper sulfides are the primary minerals. However, the formation of diopside is restricted to dry climates where circulating ground water has an alkaline pH (acidic solutions buffered by carbonates) and dissolved copper.  Dioptase is closely related to another copper silicate, chrysocolla.

And finally, dioptase may be, and has been, used as a pigment for painting.

The though for Monday:  Green is the prime color of the world, and that from which its loveliness arises.  Pedro Calderon de la Barca.