Yes, CAPIZ is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, P 3, I 1, Z 10.

Is it a valid word?

CAPIZ is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

marine bivalve common in Philippine coastal waters characterized by a large thin flat translucent shell

Also: window oyster, windowpane oyster, placuna placenta.