CUPRITE
Cuprite is a reddish- to almost black-colored, copper
oxide mineral (Cu2O). It most frequently occurs as
microcrystalline coatings on pre-existing copper metal or Cu-bearing
sulfides. It sometimes occurs as nice, bright red, lustrous, transparent
crystals ("ruby copper ore"). Cuprite may be mistaken for hematite
or cinnabar, but cuprite is always associated with copper minerals. It
occurs in the supergene zone, the near-surface portion of mineral deposits
where oxidizing conditions occur.
As native copper weathers, a coating of cuprite forms,
followed later by a black coating (tenorite). After that, cuprite and
tenorite can combine with water and atmospheric carbon dioxide to form green
coatings of malachite.
Cuprite
(reddish) on native copper (4.2 cm across) from the Portage Lake Volcanic Series
of northern Michigan, USA.
Cuprite
(blackish) on native copper from the Poteryaevskoe Mine, northwestern end of
the Altay Mountains, southwestern Siberia, Russia, north-central Asia.
The Poteryaevskoe Mine exploited the Rubtsovsk Cu-Zn-Pb Deposit, a
subaqueous, volcanogenic massive sulfide deposit in the Kamenevsk Group, upper
Frasnian Stage, ~mid-Upper Devonian. (public display, Hillman Hall of
Minerals and Gems, Carnegie Museum of Natural History, Pittsburgh,
Pennsylvania, USA) (Some info. provided by Kudryavtseva et al., 1979, Geologiya
i Razvedka 1979(10): 82-88.)