Yes, CRYSTALS is a Scrabble word!

Letter values in Scrabble US: C 3, R 1, Y 4, S 1, T 1, A 1, L 1, S 1.

Is it a valid word?

CRYSTALS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a solid formed by the solidification of a chemical and having a highly regular atomic structure
a crystalline element used as a component in various electronic devices
a rock formed by the solidification of a substance; has regularly repeating internal structure; external plane faces
colorless glass made of almost pure silica
glassware made of quartz
a protective cover that protects the face of a watch

Also: quartz glass, vitreous silica, watch crystal, watch glass.

Not playable in Scrabble US: LECHATELIERITE.