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Digital Subscriptions > Rock&Gem Magazine > November 2019 > COVELLITE


A Rare and Mysterious Contributor to Advancement

The distinction of one of the toughest copper minerals to find probably belongs to covellite, with dioptase serving as solid competition on that front. Like its more common cousins of chalcopyrite and bornite, covellite (also known as covelline) can display an unrivaled iridescence of dazzling colors usually in the realm of indigo, purple, and dark red hence its nicknames of “blue copper” and “indigo copper,” to name a few.

I, as well as at least a few others, have called it the most beautiful sulfide we have ever seen. Additionally, it is much softer than any of its copper-bearing cousins with a Mohs’ hardness of only 1.5 to 2. Speaking of common, an initial glance at its chemical formula (CuS) might not spark great conversation, but covellite’s constitution is more than skin deep.

It may come as a surprise to some, but covellite plays the runt as a practical source of copper, despite its chemical formula suggesting the mineral is 66% of the red metal. Although it leaves behind a conventional charcoalcolored streak, covellite easily stands out when viewed underneath the microscope by displaying a periwinklelight blue hue that stands out from its relatives. Also standing out is its periodically-seen hexagonal platy crystals displaying cleavage like that found in mica minerals. Pure 100% covellite is seldom-seen, but perhaps that is a wonderful thing to most copper mineral collectors.

Most specimens display a rainbow-like iridescent nature showing off dark reds and purples on an indigo backdrop, whereas others exude a royal blue and gold pairing. The heterogeneous nature arises from partial chemical weathering of primary copper minerals such as chalcocite, bornite, and chalcopyrite. In most cases, covellite forms simple, thin coatings on these and other sulfide minerals. Less often though, covellite can occur as a primary mineral, under rarer, very specific hydrothermal conditions.

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Rock & Gem November 2019, COVELLITE : Marveling over mysterious 'Indigo Copper', Ancient Beads : Evidence of Commonality among Cultures, Cornwall Mining, And More....