löllingite

{{Infobox mineral | name = Loellingite | boxwidth = | boxbgcolor = | image = Lollingite-177962.jpg | imagesize = | alt = | caption = 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 × 2.2 × 2.0 cm. | category = Arsenide mineral | formula = FeAs2 | IMAsymbol = Lö | molweight = | strunz = 2.EB.15a | dana = | system = Orthorhombic | class = Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) | symmetry = Pnnm | unit cell = a = 5.16, b = 5.93 c = 3.05 [Å]; Z = 2 | color = Steel grey to silvery white | colour = | habit = Prismatic to pyramidal crystals, massive | twinning = On {001}, possibly trillings, polysynthetic on {101} | cleavage = Rare, distinct on {010}, {101} | fracture = Uneven | tenacity = | mohs = 5–5.5 | luster = Metallic | streak = Grayish black | diaphaneity = | gravity = 7.1–7.5 | density = | polish = | opticalprop = Distinctly anisotropic in reflected light | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = }} 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.