Loellingite: Properties and Occurrences

Loellingite, also spelled löllingite, is an iron arsenide mineral with formula FeAs2. It is a mineral consisting of a tin-white iron arsenide that is isomorphous with arsenopyrite and usually occurs massive. The orthorhombic lollingite group includes the nickel-iron arsenide rammelsbergite and the cobalt iron arsenide safflorite. It is a tin-white arsenide of iron, isomorphous with arsenopyrite. Leucopyrite is an old synonym for loellingite. Their crystal forms, color, luster, streak, and fracture are all very similar.

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

General Information

  • Category: Arsenide mineral
  • Formula: FeAs2
  • Crystal system: Orthorhombic
  • Crystal class: Dipyramidal (mmm)
  • Color: Steel grey to silvery white.

Properties

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.

  • 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

Occurrences:

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

It is often found associated with arsenopyrite (FeAsS) from which it is hard to distinguish. Cobalt, nickel and sulfur substitute in the structure.

 

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