Melilite
A calcium aluminium silicate series, gehlenite to åkermanite, that makes up much of the white inclusions in Allende.
Key facts
- Formula
- (Ca,Na)2(Al,Mg)(Si,Al)2O7
- Family
- Silicates
- Crystal system
- Tetragonal
What it is
Melilite is a series of silicates built from pairs of silicon–oxygen groups. The aluminium-rich end is gehlenite and the magnesium-rich end is åkermanite. It is one of the minerals expected to form early as a hot gas of solar composition cools.
Where it is found
It is a major mineral of type A and type B calcium-aluminium-rich inclusions in CV chondrites, the oldest dated solids in the Solar System, and occurs in CAIs of other carbonaceous chondrites. On Earth it is found in rare silica-poor lavas and in blast-furnace slag.
How it is recognised
In thin section melilite is colourless with very low, anomalous blue interference colours. In cut CV chondrites the white, irregular inclusions rich in melilite stand out against the dark matrix.
Did you know?
The zoning of melilite crystals records the cooling of CAI melt droplets in the solar nebula.
Melilite is often partly replaced by nepheline and grossular in altered CAIs.