plagioclase

noun pla·gio·clase \ˈplā-j(ē-)ə-ˌklās, ˈpla-, -ˌklāz\

Definition of PLAGIOCLASE

: a triclinic feldspar; especially : one having calcium or sodium in its composition

Greek plagios oblique + klasis breaking, from klan to break — more at clast

First Known Use: circa 1868

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