Cuprite: Properties & Facts

Cuprite, also known as ruby copper due to its beautiful red color, is a fascinating mineral with a rich history and diverse uses. 

Cuprite, with its chemical formula Cu₂O, is a copper(I) oxide mineral. Its deep red color, often compared to ruby, comes from the way it absorbs specific wavelengths of light. In its natural state, it forms cubic crystals, octahedrons, or dodecahedrons, adding a geometric charm to its beauty.

Cuprite 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.

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.

Stunning Cuprite Crystals. From: Villecun, Olmet-et-Villecun, Hérault, Occitanie, France Photo by: Laurent Kbaier

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.

Properties of Cuprite

• Formula: Cu₂O
• System: Isometric
• Colour: Dark red to cochineal ...
• Lustre: Adamantine, Sub-Metallic, Earthy Crystal Habits include the cube, octahedron, dodecahedron, and combinations of these forms. Some display faces of the obscure gyroid form. A variety known as Chalcotrichite forms long needle-like crystals or fuzzy crusts. also massive.
• Cleavage is fair in four directions forming octahedrons.
• Fracture is conchoidal.
• Hardness is 3.5-4
• Specific Gravity is approximately 6.0 (very heavy for translucent minerals)
• Streak is brick red.
• Associated Minerals are limonite, copper, chrysocolla, malachite and other secondary copper minerals.
• Other Characteristics: Forms a surface film with long exposure to strong light. Crystals of cuprite are sometimes altered or partially altered to malachite and rarely copper.
• Notable Occurrences include Arizona, USA; Africa; Australia; Chile and several localities in Europe.
• Best Field Indicators are color, crystal form and softness.