Ureilite
A carbon-rich achondrite made mostly of olivine and pyroxene, with graphite and tiny diamonds squeezed between the grains.
Ureilites are among the strangest stony meteorites. They are achondrites, meaning rocks that melted on their parent body, yet they keep chemical hints of primitive material. Most are coarse-grained mixtures of olivine and a calcium-poor pyroxene called pigeonite, with dark seams of carbon running between the crystals. That carbon is mostly graphite, but shock has turned some of it into diamond.
They matter because they record a parent body that was partly melted and then smashed apart early in Solar System history, before it could fully separate into core, mantle and crust. The group takes its name from Novo-Urei, which fell in Russia in 1886. The most famous ureilite story is Almahata Sitta: in October 2008 the small asteroid 2008 TC3 was spotted in space less than a day before it exploded over Sudan, and hundreds of fragments were later collected from the desert. Many proved to be ureilites mixed with other meteorite types.
In hand, a ureilite is dark grey to black, often with a slightly greasy-looking surface where carbon fills the gaps. A cut face shows interlocking greenish-brown grains with black rims. Diamonds inside make them notoriously hard to saw.
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