1.NounSodium calcium aluminum silicate, (
N
a
x
C
a
x
A
l
S
i
3
O
8
{\displaystyle Na_{x}Ca_{x}AlSi_{3}O_{8}}
), a plagioclase feldspar, the third member of the albite-anorthite solid solution series. Found in fine-grained andesite lavas; crystals are rarely seen.