The terminating surface (or basal plane) parallel to the atom planes in the repeating layers in clays and layered minerals. Common usage has broadened the meaning to include (internal) surfaces that parallel the terminating surface. If the repeating layers have a stacking direction along [001], the c crystallographic axis, then the atom planes in the repeating layers are the (00l) planes (parallel to the plane containing the two lateral axes, a and b).
Syn., basal plane