Loellingite

Loellingite

Sharp, lustrous loellingite (and/or arsenopyrite?) crystals to 4 mm on gossan matrix. Locality: Broken Hill Ore Deposit, New South Wales, Australia. Size: 2.4 x 2.2 x 2.0 cm.
General
Category Arsenide mineral
Formula
(repeating unit)		 FeAs2
Strunz classification 2.EB.15a
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnnm
Unit cell a = 5.16, b = 5.93
c = 3.05 [Å]; Z = 2
Identification
Color Seel grey to silvery white
Crystal habit Prismatic to pyramidal crystals, massive
Twinning On {001}, possibly trillings, polysynthetic on {101}
Cleavage Rare, distinct on {010}, {101}
Fracture Uneven
Mohs scale hardness 5-5.5
Luster Metallic
Streak Grayish black
Specific gravity 7.1-7.5
Optical properties Distinctly anisotropic in reflected light
References [1][2][3]

Loellingite, also spelled löllingite, is an iron arsenide mineral with formula FeAs2. It is often found associated with arsenopyrite (FeAsS) from which it is hard to distinguish. Cobalt, nickel and sulfur substitute in the structure. The orthorhombic lollingite group includes the nickel iron arsenide rammelsbergite and the cobalt iron arsenide safflorite. Leucopyrite is an old synonym for loellingite.

It forms opaque silvery white orthorhombic prismatic crystals often exhibiting crystal twinning. It also occurs in anhedral masses and tarnishes on exposure to air. It has a Mohs hardness of 5.5 to 6 and a quite high specific gravity of 7.1 to 7.5. It becomes magnetic after heating.

Loellingite was first described in 1845 at the Lölling district in Carinthia, Austria, for which it was named.

It occurs in mesothermal ore deposits associated with skutterudite, native bismuth, nickeline, nickel-skutterudite, siderite and calcite. It has also been reported from pegmatites.[3]

Loellingite from Franklin-Sterling (size: 10.4 x 7.0 x 6.8 cm)

References

  1. ↑ Mindat
  2. ↑ Webmineral
  3. 1 2 Handbook of Mineralogy

Further reading

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