plagioclase feldspar
Technical mineralogy term for a series of feldspar minerals. Not common in everyday conversation.
Plagioclase feldspar is a mineral commonly found in igneous rocks.
From 斜 (しゃ, 'oblique') + 長石 (ちょうせき, 'feldspar'), referring to the oblique cleavage angles characteristic of plagioclase feldspar.