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CUPRITE, a mineral consisting of cuprous oxide, Cu2O, crystallizing in the cubic system, and forming an important ore of copper, of which element cuprite contains 88.8%.

Faces of a pentagonal icositetrahedron with high indices have been very rarely observed on crystals of cuprite, potassium chloride and ammonium chloride, but none of these are circular polarizing.

The minerals associated with the quartz in this vein, especially the cuprite and mispickel, are found most abundantly upon the foot-wall side, or underside of the quartz itself.

The etching figures do not, however, conform to this lower degree of symmetry, nor do crystals of cuprite rotate the plane of polarization of plane-polarized light.