Plagioclase
A feldspar mineral, rich in calcium or sodium, that forms the pale grains in many achondrites and lunar rocks.
Plagioclase is a type of feldspar, the most common mineral group in Earth's crust. Plagioclase is made of aluminium, silicon and oxygen with either sodium or calcium, or a mixture of both. The sodium-rich end is called albite and the calcium-rich end is called anorthite.
In meteorites, plagioclase helps tell the story of melting. In basaltic achondrites, such as the eucrites Juvinas and Millbillillie, calcium-rich plagioclase crystallised from lava alongside pyroxene. The bright highlands of the Moon are made largely of anorthite-rich rock, so pale lunar meteorites are full of it. In ordinary chondrites, sodium-rich plagioclase grows from glass as the rock is heated inside its parent asteroid, and the size of those grains helps scientists assign a petrologic type. A strong impact can turn plagioclase into a glass called maskelynite.
Plagioclase is usually white, grey or colourless. In a cut eucrite it appears as pale, lath-shaped crystals between darker pyroxene grains. It is not magnetic. As always, do not cut, heat or use acid on samples yourself; let a trained adult or a lab handle that work.
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Level: Explorer Ages 10 and up