Blue crystals of the rare mineral cualstibite-1M from the famous Clara mine (Wolfach, Black Forest, Baden-Württemberg, Germany). Previously known as cyanophyllite but renamed as cualstibite-1M in 2012. — Photo: David Hospital · CC BY-SA 4.0
Cualstibite
Cualstibite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Cu₂Al(OH)₆[Sb(OH)₆].
It crystallizes in the hexagonal crystal system (space group P-3). It is a member of the Hydrotalcite structural group.
Key properties: Mohs hardness 2; specific gravity 3.18; Pale blue streak; Vitreous luster; optically uniaxial.
IMA symbol Casb, IMA status: approved, named in 1983.
A secondary mineral from oxidation of a hydrothermal polymetallic barite–fluorite deposit.
It is found associated with Cornwallite, arsenogoyazite, goethite, barite, fluorite, quartz.
The name comes from the chemical symbols of the mineral’s major components, copper (CUprum), ALuminum, and antimony (STIBium).