Forsterite
The magnesium-rich end of the olivine series, the olivine of primitive chondrules and the oldest Solar System grains.
Key facts
- Formula
- Mg2SiO4
- Family
- Silicates
- Crystal system
- Orthorhombic
What it is
Forsterite is olivine in which almost all the metal sites hold magnesium. It melts at about 1,890 °C, higher than almost any other common silicate, and it is one of the first silicates expected to condense from a cooling gas of solar composition.
It is named after Adolarius Jacob Forster, an eighteenth-century English mineral dealer.
Where it is found
Nearly pure forsterite occurs in the chondrules of unequilibrated carbonaceous chondrites such as CV, CO and CM chondrites, in amoeboid olivine aggregates, and in enstatite-rich meteorites. Comet Wild 2 dust and some interplanetary dust particles hold forsterite grains, and space telescopes detect its glow in the discs of dust around young stars.
How it is recognised
It is colourless to pale green and shows olivine's bright interference colours in thin section. Under an electron beam, magnesium-rich forsterite often glows red, a property called cathodoluminescence that helps find the most primitive grains in a chondrite.
Did you know?
Telescopes have detected crystalline forsterite in the dust of comets and around other stars.
Some forsterite grains in chondrites contain oxygen isotopes almost identical to those in the Sun.