Yes, TAMARACK is a Scrabble word!

Letter values in Scrabble US: T 1, A 1, M 3, A 1, R 1, A 1, C 3, K 5.

Is it a valid word?

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

medium-sized larch of Canada and northern United States including Alaska having a broad conic crown and rust-brown scaly bark

Also: american larch, black larch, larix laricina.