Ureilites

A complex history

Ureilites combine evidence of igneous processing, primitive components and an intense impact history. Their original parent body is not definitively identified.

Olivine, pyroxene and carbon

Ureilites consist mainly of olivine and low-calcium pyroxene with carbon-rich material between grains. Carbon occurs partly as graphite; high impact pressures can produce microscopic diamonds.

Olivine grain margins commonly record reduction reactions that removed iron from the silicate. These features reflect an unusual chemical environment, not biological carbon.

A partly melted and disrupted body

Ureilites are considered primitive achondrites: their parent body became hot enough for partial melting and separation, yet retained some primitive chemical signatures. Major collisions later disrupted it.

Monomict ureilites are dominated by one rock type. Polymict ureilites are breccias containing different ureilitic and foreign fragments. This combination explains why the group shows both igneous and primitive characteristics.