- Lower boundary of zone
of concentric folding.
Source: Leet, L. Don. 1982.
Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
- a. A plane perpendicular to the c, or principal, axis in a tetragonal or
hexagonal structure. ASM, 1
b. Syn: basal pinacoid
Dictionary of Mining, Mineral, and Related Terms