Diogenite
An achondrite made mostly of magnesium-rich orthopyroxene, thought to come from deep in the crust of Vesta.
Diogenites are the deep-seated member of the HED family. Where eucrites are lavas, diogenites are coarse rocks built almost entirely from orthopyroxene, a calcium-poor pyroxene rich in magnesium, with minor olivine, chromite and plagioclase. They are thought to have crystallised slowly in bodies of magma beneath Vesta's surface, with pyroxene crystals settling or growing in large masses.
They help planetary scientists reconstruct how Vesta's interior formed. The group is named after Diogenes of Apollonia, an ancient Greek thinker who suggested that some stones come from the sky. The classic example is Tatahouine, which fell in Tunisia in 1931 and broke into many small, bright green fragments. Johnstown, which fell in Colorado in 1924, is another well-studied diogenite. Rocks rich in diogenite-like pyroxene were also mapped around the Rheasilvia basin by the Dawn spacecraft.
Most diogenites are breccias of angular pyroxene fragments. Their colour is distinctive: pale greenish-yellow to deeper green, much brighter than a typical eucrite. The fusion crust is often thinner and less glossy. As with all meteorites, home tests should stop at looking and using a magnet; leave cutting and chemical testing to experienced adults.
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