Burgessite
Burgessite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Co₂(H₂O)₄[AsO₃(OH)]₂(H₂O).
It crystallizes in the monoclinic crystal system (space group P2_122). It is a member of the Burgessite structural group.
Key properties: Mohs hardness 3; specific gravity 2.93; Colorless to pale pink streak; Vitreous to adamantine luster; optically biaxial.
IMA symbol Bge, IMA status: approved, named in 2007.
A secondary mineral along fractures in the weathering zone of a polymetallic sulfarsenate deposit.
It is found associated with Skutterudite, cobaltite, bismuth, arsenolite, bismuthoferrite, erythrite.
The name refers to David Burgess (b. 1951), of Newington, Connecticut, USA, who brought the sample to the authors’ attention.