Majorite
A garnet made from pyroxene at high pressure, in which silicon takes an unusual place.
Key facts
- Formula
- Mg3(MgSi)(SiO4)3
- Family
- High-pressure minerals
- Crystal system
- Cubic
- First described
- the Coorara L6 chondrite, 1970
Majorite was first found in 1970 in the Coorara meteorite, an L6 chondrite found in Western Australia. It is named after Alan Major, who helped with the high-pressure experiments that produced it.
What it is
Majorite has the garnet structure, but some of the sites normally filled by aluminium hold magnesium and silicon instead. It forms when pyroxene is squeezed to pressures above about 15 gigapascals.
In Earth's mantle, pyroxene is thought to turn gradually into majorite-rich garnet below about 300 kilometres.
Where it is found
It occurs in shock veins in heavily shocked chondrites, often crystallised from shock melt together with ringwoodite. It is also found as inclusions in some diamonds that grew deep in Earth's mantle.
How it is recognised
It is colourless to pale and fine-grained. Raman spectroscopy and microprobe analysis identify it.
Did you know?
The composition of majorite grains in a shock vein helps estimate the peak pressure of the impact.
Majorite inclusions in diamonds come from more than 300 kilometres below Earth's surface.