Most common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences.
- Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after the core and the mantle had already been formed.
- Cumulate eucrites are the products of gravitational settling of crystallized minerals, mainly pyroxene and plagioclase, within magma chambers trapped below the early crust.
- Polymict eucrites are breccias that contain over 90% eucritic material and less than 10% diogenitic clasts. This 9:1 ratio is an arbitrary criterion to discriminate between polymict eucrites and the closely related howardites that contain more than 10% diogenitic clasts with eucritic material comprising the rest of the meteorite.
Some or all content above used with permission from J. H. Wittke.