Johnbaumite
A calcium arsenate-hydroxide apatite-group mineral — found at Harstigen, Sweden in the 1800s but mistaken for svabite until 1980.
Intro adapted from Wikipedia (CC BY-SA).
Johnbaumite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₅(AsO₄)₃(OH).
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Apatite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.68; White streak; Adamantine to greasy on fracture surfaces, vitreous on cleavage surfaces luster; optically uniaxial.
IMA symbol Jbm, IMA status: approved, named in 1980.
A very rare mineral, part of a metamorphic skarn assemblage in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA).
It is found associated with Yeatmanite, diopside, andradite, franklinite, copper, roméite (Franklin, New Jersey, USA); tilasite, andradite, calcite, caryopilite (Långban, Sweden).
The mineral was named to honor John L. Baum (1916-2011), Hamburg, New Jersey, USA, former Curator of the Franklin Mineral Museum and collector of the first specimen containing the mineral.