— plagioclastic /play'jee euh klas"tik/ , adj.
/play"jee euh klays'/ , n.
any of the feldspar minerals varying in composition from acidic albite, NaAlSi 3 O 8 , to basic anorthite, CaAl 2 Si 2 O 8 , found in most igneous rocks: shows twinning striations on good cleavage surfaces. Also called soda-lime feldspar .
[ 1865-70; PLAGIO- + -CLASE ]