2.2" Glassy Quartz Crystals over Plancheite - Sanda, Congo

Plancheite is a rare, hydrated copper silicate mineral that is typically found in oxidized copper deposits. It is a colorful mineral with a silky luster that can range in color from pale blue to deep blue or pale greenish blue, often forming fibrous or compact radial aggregates in association with other secondary copper minerals (chrysocolla, dioptase, malachite, shattuckite, and brochantite).

Plancheite is named after François Gilbert Planche, a French industrialist, politician, and director of the French Congo Mining Company. Planche provided the original samples of plancheite for study.

Chemical formula: Cu₈Si₈O₂₂(OH)₄

About Quartz

Quartz is the name given to silicon dioxide (SiO2) and is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich environments--usually igneous rocks or hydrothermal environments like geothermal waters--at temperatures between 100°C and 450°C, and usually under very high pressure. In either case, crystals will precipitate as temperatures cool, just as ice gradually forms when water freezes. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountain formation: these veins can be hundreds of millions of years old.