Glaucodot

Glaucodot is a cobalt iron arsenic sulfide mineral with formula (Co,Fe)AsS. The cobalt:iron(II) ratio is typically 3:1 with minor nickel substituting. It forms a series with arsenopyrite (FeAsS). It is an opaque grey to tin-white typically found as massive forms without external crystal form. It crystallizes in the orthorhombic system. The locality at Håkansboda, Sweden has rare twinned dipyramidal crystals (see photo). It is brittle with a Mohs hardness of 5 and a specific gravity of 5.95. It occurs in high temperature hydrothermal deposits with pyrrhotite and chalcopyrite. Glaucodot is classed as a sulfide in the arsenopyrite löllingite group.

Glaucodot
Glaucodot from Håkansboda, Lindesberg, Sweden. Size: 3.3 x 2.7 x 2.6 cm.
General
Category	Sulfide minerals
Formula (repeating unit)	(Co,Fe)AsS (Co0.75Fe2+0.25AsS)
IMA symbol	Gl[1]
Strunz classification	2.EB.10c
Crystal system	Orthorhombic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Identification
Formula mass	165.15 g/mol
Color	Grayish tin white, Reddish silver white
Crystal habit	Massive , prismatic habits with elongated sphenoids, granular masses- Uniformly indistinguishable crystals forming large masses.
Cleavage	None
Fracture	Brittle - Uneven - Very brittle fracture producing uneven fragments.
Mohs scale hardness	5
Luster	Metallic
Streak	black
Diaphaneity	Opaque
Specific gravity	5.9 - 6.01, Average = 5.95
Ultraviolet fluorescence	inert
Other characteristics	Nonmagnetic, non-radioactive

Glaucodot was first described in 1849 in Huasco, Valparaíso Province, Chile. Its name originates from the Greek Ancient Greek: γλανκός ("blue") in reference to its use in the dark blue glass called smalt.