Nepheline
A sodium aluminium silicate that replaces melilite and anorthite in CAIs that were later altered.
Key facts
- Formula
- (Na,K)AlSiO4
- Family
- Silicates
- Crystal system
- Hexagonal
What it is
Nepheline is a feldspathoid: a framework silicate like feldspar but with less silica. It forms in rocks too poor in silica for feldspar, or where sodium is added. Its name comes from the Greek for cloud, because it turns cloudy in acid.
Where it is found
In CV chondrites such as Allende it is common in the outer parts of calcium-aluminium-rich inclusions and in chondrules, together with sodalite. It formed when sodium-rich fluids or gases attacked the primary minerals melilite and anorthite. It also occurs in some ordinary chondrite chondrules.
How it is recognised
It is colourless to grey and usually very fine-grained in meteorites. It is identified by its chemistry, rich in sodium and aluminium, with an electron microprobe or electron microscope.
Did you know?
The alteration that made nepheline in Allende CAIs disturbed some of their isotope clocks.
Nepheline is mined on Earth for making glass and ceramics.