Grossular
A calcium aluminium garnet that grows in altered refractory inclusions of carbonaceous chondrites.
Key facts
- Formula
- Ca3Al2(SiO4)3
- Family
- Silicates
- Crystal system
- Cubic
What it is
Grossular is a garnet: a silicate whose isolated silicon–oxygen groups are linked by calcium and aluminium. It is often pale green or orange, and its name comes from the Latin for gooseberry. On Earth it forms mainly when limestone is heated by nearby magma.
Where it is found
In meteorites it is a secondary mineral. It grows with sodalite, nepheline and anorthite where fluids altered the melilite of calcium-aluminium-rich inclusions in CV chondrites such as Allende. It also occurs with andradite, its iron partner, in altered chondrules.
How it is recognised
It is identified by its composition and its isotropic appearance under crossed polars, typical of garnets.
Did you know?
Tsavorite, a prized green gemstone, is a form of grossular.
Meteorite garnets are mostly microscopic, unlike the large crystals found on Earth.