Glaucodot

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Glaucodot
Glaucodot-169959.jpg
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)
Strunz classification 02.EB.10c
Identification
Formula mass 165.15
Color Grayish tin white, Reddish silver white
Crystal habit Massive - Uniformly indistinguishable crystals forming large masses.
Crystal system Orthorhombic (2/m 2/m 2/m) Space Group: C mmm
Cleavage None
Fracture Brittle - Uneven - Very brittle fracture producing uneven fragments.
Mohs scale hardness 5
Luster Metallic
Streak black
Specific gravity 5.9 - 6.01, Average = 5.95
Ultraviolet fluorescence inert
Other characteristics Nonmagnetic, non-radioactive

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

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