Sanakirja.org

(mineralogy) An orthorhombic-disphenoidal mineral containing copper, hydrogen, oxygen, and tellurium.

Sky-blue, cobalt-blue, bluish gray, bright blue to greenish blue in transmitted light. Prismatic or flattened crystals, Sometimes as crusts or aggregates – Distinct – Brittle – Brittle – 2.5 – Vitreous, dull – Light blue – Semitransparent – 3.8 – Biaxial (−) – Δ = 0.024 – Various shades of blue – 36° – Fusible, gives a black bead – Insoluble – Sulfur.