Olivine is a mineral formed from
silica tetrahedra with magnesium (Mg
+2) ions, or some other metal ion like manganese, iron, or calcium, in
octahedral positions.
Olivine is one of the most important of the minerals making up the Earth. Olivines are a major constituent of the
ultrabasic rocks (
peroditites) in the upper part of the
Earth's
Mantle. They are to
Gabbro and
Basalt what
Feldspars are to
Granite and
Rhyolite.
The olivine minerals include:
Forsterite (Mg
2SiO
4) (see
Peridot)
Tephroite (Mn
2SiO
4)
Fayalite (Fe
2SiO
4)
Monticellite (CaMgSiO
4)