Brown crystals of the very rare beryllium mineral bergslagite from the type locality in the famous Langban deposit (Langban, Värmland, Sweden). It has an old label from the F.Bauer collection. — Photo: David Hospital · CC BY-SA 4.0
Bergslagite
Bergslagite is an IMA-recognized mineral species in the arsenate class, with the chemical formula CaBe(AsO₄)(OH).
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Gadolinite structural group.
Key properties: Mohs hardness 5; specific gravity 3.4; Vitreous to greasy luster; optically biaxial.
IMA symbol Bgl, IMA status: approved, named in 1983.
Found in thin veins in pieces of hematite ore found on mine dumps from a metamorphosed Fe–Mn orebody (Långban, Sweden); in rhyolite (Sailauf, Germany).
It is found associated with Manganoan diopside, manganberzeliite, tilasite, svabite, hematite, calcite, barite (Långban, Sweden); hematite, muscovite (Sailauf, Germany).
The name refers to the occurrence at Långban, which is in the Bergslagen region of Sweden.