Mineral description : Forsterite

Mineral class Silicates : Nesosilicates : Olivine group

Chemical formula (Mg,Fe)₂(SiO₄)

Crystal system Orthorombic

Habitus Thick tabular dipyramidal crystals, frequently with wedge-shaped terminations. Mostly as grains or massive aggregates.

Cleavage [001] good and [010] distinct, fracture conchoidal.

Hardness 6.5 - 7

Density 3.21 - 3.33

Color Green to greenish yellow or colorless, also brown, pale red, gray or bluish gray.

Streak Colorless

Luster Vitreous to greasy, transparent.

Description Forsterite is the magnesium rich member of the olivine series. When the iron contents increases over 50% it turns into fayalite.

Occurance Forms in basic and ultrabasic igneous rocks (gabbro, pyroxenite or peridotite). Also formed in marbles.

Associates

Notes Clear gemmy olivine is called peridote. Other names used for forsterite is chrysolite and olivine.
Type Locality : Monte Somma, Vesuvio (Vesuvius), Napoli, Campania, Italy.
Discovered in 1824.
Named after Adolarius Jacob Forster (1739-1806).
Forsterite is soluble in hydrochloric acid with gelatinisation.

Localities A common mineral and a major part of many rocks.
Sweden :

Gransjöbleriken, Vilhelmina, Lappland. (Ref. GFF 55, 323)
Långban, Filipstad, Värmland. (Ref. GFF 46, 285)
Odalfältet, Nordmark, Filipstad, Värmland. (Ref. SGU Ca13, 36)
Kaveltorp, Ljusnarsberg, . (Ref. SGU Ca30, 83)
Fredgåsberget, Leksand, Dalarna. (Ref. SGU Ca35, 503)
Gruvåsen, Persberg, Värmland. (Ref. Kommerskoll 2, 70)
Stabbygruvan, Norrtälje, Uppland.
... Plus a number of other localities.
Norway :

Dypingdalen, Snarum. In a serpentinite - magnesite occurance.
Langöya, Vesterålen.
Forsterite is much more common than fayalite in Norway. Most dunites consists of forsterite.
Finland : (Sorry if the names are messed up, but I don't speak Finnish)

Sahakoski, Ahlainen.
Laukunkangas, Enonkoski. In peridotite - olivine gabbro.
Näätäniemi serpentine massif, Kuhmo greenstone belt.
Näränkävaara, Kuusamo. In gabbro and norite.
Ihalainen, Lappeenranta. In limestone.
.. Plus a number of other localities.

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Last changed : 2001-03-17

Mineral class	Silicates : Nesosilicates : Olivine group
Chemical formula	(Mg,Fe)₂(SiO₄)
Crystal system	Orthorombic
Habitus	Thick tabular dipyramidal crystals, frequently with wedge-shaped terminations. Mostly as grains or massive aggregates.
Cleavage	[001] good and [010] distinct, fracture conchoidal.
Hardness	6.5 - 7
Density	3.21 - 3.33
Color	Green to greenish yellow or colorless, also brown, pale red, gray or bluish gray.
Streak	Colorless
Luster	Vitreous to greasy, transparent.
Description	Forsterite is the magnesium rich member of the olivine series. When the iron contents increases over 50% it turns into fayalite.
Occurance	Forms in basic and ultrabasic igneous rocks (gabbro, pyroxenite or peridotite). Also formed in marbles.
Associates
Notes	Clear gemmy olivine is called peridote. Other names used for forsterite is chrysolite and olivine. Type Locality : Monte Somma, Vesuvio (Vesuvius), Napoli, Campania, Italy. Discovered in 1824. Named after Adolarius Jacob Forster (1739-1806). Forsterite is soluble in hydrochloric acid with gelatinisation.
Localities	A common mineral and a major part of many rocks. Sweden : Gransjöbleriken, Vilhelmina, Lappland. (Ref. GFF 55, 323) Långban, Filipstad, Värmland. (Ref. GFF 46, 285) Odalfältet, Nordmark, Filipstad, Värmland. (Ref. SGU Ca13, 36) Kaveltorp, Ljusnarsberg, . (Ref. SGU Ca30, 83) Fredgåsberget, Leksand, Dalarna. (Ref. SGU Ca35, 503) Gruvåsen, Persberg, Värmland. (Ref. Kommerskoll 2, 70) Stabbygruvan, Norrtälje, Uppland. ... Plus a number of other localities. Norway : Dypingdalen, Snarum. In a serpentinite - magnesite occurance. Langöya, Vesterålen. Forsterite is much more common than fayalite in Norway. Most dunites consists of forsterite. Finland : (Sorry if the names are messed up, but I don't speak Finnish) Sahakoski, Ahlainen. Laukunkangas, Enonkoski. In peridotite - olivine gabbro. Näätäniemi serpentine massif, Kuhmo greenstone belt. Näränkävaara, Kuusamo. In gabbro and norite. Ihalainen, Lappeenranta. In limestone. .. Plus a number of other localities.