planchéite

Planchéite is a rare copper silicate mineral with the chemical formula Cu2+10(Si5O16)(OH)2. It is found in oxidized zones of copper deposits, often associated with other copper minerals like chrysocolla, malachite, and azurite. Planchéite typically occurs as fibrous or radiating aggregates, forming botryoidal or reniform masses. Its color ranges from intense azure blue to deeper shades of blue, sometimes exhibiting greenish tints. The mineral is known for its striking color and is sought after by collectors.

The name planchéite honors the French mineralogist and crystallographer Jean-Baptiste Louis Romé de l'Isle, whose work was crucial in the early development of crystallography. However, the mineral was actually named after the French mineral collector Hippolyte Planché, who discovered it in the Republic of the Congo in 1908. The type locality is the Katanga Mine in the Katanga Province of the Democratic Republic of Congo.

Planchéite has a relatively low hardness, typically around 4.5 to 5 on the Mohs scale, and a specific gravity of about 3.5. It is an opaque mineral, often showing a vitreous to silky luster. Due to its rarity and attractive color, planchéite is primarily valued as a mineral specimen. While it is a copper-bearing mineral, it is not economically significant as a source of copper due to its limited occurrence and difficulty in extraction. Its geological formation is thought to be the result of hydrothermal alteration processes in copper-rich environments.