Cafarsite

Cafarsite (Ca
₈(Ti,Fe²⁺
,Fe³⁺
,Mn)
_6–7(AsO
₃)
₁₂·4H
₂O) is a rare calcium iron arsenite mineral. Manganese and titanium occur with iron in the formula.

Cafarsite
Cafarsite on granite
General
Category	Arsenites
Formula	Ca 8(Ti,Fe2+ ,Fe3+ ,Mn) 6–7(AsO 3) 12·4H 2O
IMA symbol	Caf[1]
Strunz classification	4.JC.05
Crystal system	Isometric
Crystal class	Diploidal (m3) H–M Symbol (2/m 3)
Space group	Pn3
Unit cell	a = 15.984 Å; Z = 4
Identification
Formula mass	2,230.31 g/mol
Color	Dark brown
Crystal habit	Cubic/octahedral crystals
Fracture	Conchoidal
Mohs scale hardness	5+1⁄2 - 6
Luster	sub-metallic
Streak	Yellow brown
Diaphaneity	Translucent to opaque
Specific gravity	3.9
Optical properties	Isotropic
Refractive index	n = 2.2
References	[2][3][4]

It was first described in 1966 for an occurrence in the Binn Valley, Valais, Switzerland. Its name is from the composition, calcium, ferrum (iron), and arsenic.^[3][2][4] It has also been reported from Piedmont, Italy and the Hemlo gold mine in the Thunder Bay District, Ontario, Canada.^[4][3]