Chlorapatite
A chlorine-bearing calcium phosphate in ordinary chondrites, and a record of water and gas in their parent bodies.
Key facts
- Formula
- Ca5(PO4)3Cl
- Family
- Phosphates
- Crystal system
- Hexagonal
What it is
Chlorapatite is a member of the apatite group, which also includes the fluorapatite of tooth enamel. Its structure has a channel that can hold chlorine, fluorine or hydroxyl. Measuring which of these is present, and their isotopes, reveals the volatile chemistry of the rock.
Where it is found
It occurs in equilibrated ordinary chondrites, often next to merrillite, where it probably grew during heating as chlorine-rich fluids moved through the rock. Apatite with hydroxyl in lunar basalts and Martian meteorites has been used to estimate the water content of their magmas.
How it is recognised
It is colourless and identified with a microprobe, which measures chlorine, fluorine and phosphorus.
Did you know?
Apatite in lunar rocks helped overturn the old view that the Moon's interior is completely dry.
Chlorapatite in chondrites can be dated by uranium–lead and by the decay of iodine and plutonium.