Albite
Sodium-rich plagioclase feldspar, which grows in ordinary chondrites as they are heated inside their parent asteroids.
Key facts
- Formula
- NaAlSi3O8
- Family
- Silicates
- Crystal system
- Triclinic
What it is
Albite is the sodium end of the plagioclase series, with no extra aluminium. Its name comes from the Latin for white.
Where it is found
In type 4 to 6 ordinary chondrites, fine-grained albite-rich plagioclase crystallises from the glassy mesostasis of chondrules as the rock is heated. It also occurs in enstatite chondrites, in some primitive achondrites and in igneous clasts in breccias. Its high-pressure form, lingunite, is found in heavily shocked chondrites.
How it is recognised
It is white and usually fine-grained. In thin section it shows low interference colours and twinning, and a microprobe gives anorthite contents below about An15.
Did you know?
Albite in meteorites can be dated by its argon, because it holds potassium.
Shock can melt albite, and the melt then crystallises into the dense mineral lingunite.