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Cuprite Mineral Facts:

Chemical Formula: Cu₂O 88.8% Copper by weight.
Sometimes called Ruby Copper.

Colors: Red to ruby red shades often with a metallic shine. Streak is brownish-red

Hardness: 3.5 to 4.0

Density: 6.1

Cleavage: distinct, one direction.

Crystallography: Isometric

Luster:. Metallic to adamantine in clear crystals.

Optics: (Refractive Index):  2.85

Composition, Structure and Associated Minerals:
An important ore of copper of secondary origin. Found in the upper, oxidized portions of copper veins, associated with the other secondary copper minerals, native copper, malachite, azurite, chrysocolla, etc. Cuprite often occurs as well defined crystals embedded in certain sedimentary rocks in the upper, oxidized portions of copper veins, and in masses in the midst of other copper ores, from which it was produced by oxidation processes. Cuprite suffers alteration very readily. It may be reduced to native copper, in which case the copper pseudomorphs the cuprite, or, on exposure to the air it may be changed into the carbonate, malachite, pseudomorphs of which after cuprite are common.

Identification and Diagnostics
Cuprite is usually determined by its color and streak. It may easily be distinguished from other minerals possessing a red streak by the reaction for copper such as the production of a metal globule on charcoal, and the formation of cuprous chloride in concentrated hydrochloric acid solutions by the addition of water. Moreover, the mineral is softer than hematite and harder than reaglar, cinnabar and proustite. Easily fusible at 3, giving emerald-green flame, or, if moistened with hydrochloric acid and then heated, flame is azure-blue (test for copper).

Occurrence, Localities and Origins:
It is found as crystals in Thuringia, in Tuscany, on the island of Elba, in Cornwall, Eng., at Chessy, France; and near Coquimbo, in Chile. In Chile, in Peru, and in Bolivia it exists in great masses. It is also found in the Urals in Russia.

In the United States it occurs at Cornwall, Lebanon Co., Penn. It is also found associated with the native copper from Lake Superior at Keweenaw Point, Mich.; at the copper mines in St. Genevieve Co., Mo.; Found in connection with the copper deposits in Arizona. Fine crystals come from Bisbee, and at other places in Arizona. The fibrous variety  is beautifully developed at Morenci in the same State. Cuprite is mined with- other copper compounds as an ore of copper.

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