Cuprite
has been a major ore of copper and is still mined in many places
around the world. Of all the copper ores except for native copper,
cuprite gives the greatest yield of copper per molecule since there
is only one oxygen atom to every two copper atoms. As a mineral
specimen, cuprite shows fine examples of well-developed cubic crystal
forms. Cuprite's dark crystals show internal reflections of the
true deep red inside the almost black crystal. Other varieties,
such as chalcotrichite, show tufts of needle-like crystals that
have a beautiful red color and a special sparkle that make them
popular display cabinet specimens.
Its dark crystals
with red internal reflections are in the isometric 
system
hexoctahedral class, appearing as cubic, octahedral, or dodecahedral
forms, or in combinations. Penetration twins frequently occur. In
spite of its nice color it is rarely used for jewelry because of
its low Mohs hardness of 3.5 to 4. It has a relatively high specific
gravity of 6.1, imperfect cleavage and a brittle to conchoidal fracture.
The luster is sub-metallic to brilliant adamantine. The "chalcotrichite"
variety typically shows greatly elongated (parallel to [001]) capillary
or needle like crystals forms.
It
is a secondary mineral which forms in the oxidized zone of copper
sulfide deposits. It frequently occurs in association with native
copper, azurite, chrysocolla, malachite, tenorite and a variety
of iron oxide minerals. It is known as ruby copper due to its distinctive
red color.
Cuprite was
first described in 1845 and the name derives from the Latin cuprum
for its copper content.
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