Yes, MATERIALISM is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, T 1, E 1, R 1, I 1, A 1, L 1, I 1, S 1, M 3.

Is it a valid word?

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

a desire for wealth and material possessions with little interest in ethical or spiritual matters
(philosophy) the philosophical theory that matter is the only reality