Maskelynite
Plagioclase feldspar turned to glass by shock, without melting, while keeping its crystal shape.
Key facts
- Formula
- (Na,Ca)(Si,Al)4O8 (glass)
- Family
- High-pressure minerals
- Crystal system
- None (a glass)
- First described
- the Shergotty Martian meteorite, 1872
Maskelynite was described in 1872 from the Shergotty meteorite by the Austrian mineralogist Gustav Tschermak, who named it after the British mineralogist Nevil Story-Maskelyne. It is a glass rather than a true mineral, but the name is still used.
What it is
Maskelynite is feldspar whose ordered crystal structure was destroyed by a shock wave at pressures of roughly 25 to 45 gigapascals. Unlike glass made by melting, it keeps the shapes and outlines of the original crystals, so it looks like feldspar but behaves optically like glass.
Whether it forms entirely in the solid state, or by a brief melting under pressure, is still debated.
Where it is found
It is typical of shergottites, almost all of which contain maskelynite, and is common in strongly shocked chondrites, eucrites and lunar meteorites.
How it is recognised
Under crossed polarisers in a microscope, maskelynite is dark in every position, because glass does not split light, yet it still has the shapes of feldspar laths.
Did you know?
Its presence in nearly all shergottites shows how violent the impacts that launched them from Mars were.
Gas trapped in shock glass in the shergottite EETA 79001 proved that these meteorites come from Mars.