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.