Mineral description : Fayalite

Mineral class Silicates : Nesosilicates : Olivine group
Chemical formula (Fe,Mg)2(SiO4)
Crystal system Orthorombic
Habitus Thick tabular dipyramidal crystals, frequently with wedge-shaped terminations. Mostly as grains or massive aggregates.
Cleavage Imperfect, fracture conchoidal.
Hardness 6.5 - 7
Density 3.3 - 3.5
Color Green to greenish yellow or colorless.
Streak Colorless
Luster Vitreous to greasy, transparent.
Description Fayalite is the iron rich member of the olivine series. When the magnesium contents increases over 50% it turns into forsterite.
Occurance Forms in rapidly cooled acidic igneous rocks.
Associates  
Notes Clear gemmy olivine is called peridote.
Olivine is soluble in hydrochloric acid with gelatinisation.
Localities Not so common in Scandinavia, mostly found as small grains.

Sweden :

  • Mansjöberg mine, Los, Hälsingland. In eulysite with phlogopite and grunerite.
  • Käymäjärvi, Pajala area, Norrbotten.
  • Almunge, Uppsala, Uppland.
  • Friningen, Strömsund, Jämtland.
  • Garpenberg North, Garpenberg, Dalarna.
  • Muruhatten, Strömsund, Jämtland.
  • Nordingrå, Kramfors, Ångermanland.
Norway :
  • Bjerkreim - Sogndal area.
  • Sirdal - Örsdal area. In pyroxen syenites.
  • Holands hamn, Raftsund, Lofoten.
  • East side of Naverfjord, Stavern. As aggregates in larvikite.
Finland :
  • Tarkin, Eurajoki. In granite.
  • Skårskärin, Houtskarin.
  • Köyliön Riuttamaan. In iron ore.
  • Ihalaisten, Lappeenranna. In diabase.

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Last changed : 2001-03-13