Cumulate
A cumulate is an igneous rock formed when crystals settle and pile up in a body of magma.
A cumulate forms when crystals growing in a magma chamber or lava lake sink or float and gather in a layer. Because these crystals separated from the rest of the melt, a cumulate has a chemistry quite different from the magma it came from.
Several meteorite types are cumulates. Cumulate eucrites, such as Moore County and Serra de Magé, are made of pyroxene and plagioclase crystals that accumulated in Vesta's crust. Diogenites are largely orthopyroxene cumulates from deeper levels. Nakhlites from Mars are augite cumulates, and chassignites are olivine cumulates. On the Moon, the bright anorthosite crust formed as plagioclase crystals floated to the top of a global magma ocean.
Cumulates often show crystals lined up or touching one another with only a little trapped melt between them. Their trace element patterns, such as a positive europium anomaly in plagioclase-rich cumulates, help identify them and reveal the composition of the parent melt.
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