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
CategorySulfide minerals
Formula
(repeating unit)
(Co,Fe)AsS (Co0.75Fe2+0.25AsS)
Strunz classification2.EB.10c
Crystal systemOrthorhombic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Identification
Formula mass165.15 g/mol
ColorGrayish tin white, Reddish silver white
Crystal habitMassive , prismatic habits with elongated sphenoids, granular masses- Uniformly indistinguishable crystals forming large masses.
CleavageNone
FractureBrittle - Uneven - Very brittle fracture producing uneven fragments.
Mohs scale hardness5
LusterMetallic
Streakblack
DiaphaneityOpaque
Specific gravity5.9 - 6.01, Average = 5.95
Ultraviolet fluorescenceinert
Other characteristicsNonmagnetic, non-radioactive

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.

References

  • Webmineral:Glaucodot
  • Mindat with location data
  • Scandinavian mineral gallery
  • Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., p. 288, ISBN 0-471-80580-7


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