Yes, GALLIUM is a Scrabble word!

Letter values in Scrabble US: G 2, A 1, L 1, L 1, I 1, U 1, M 3.

Is it a valid word?

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

a rare silvery (usually trivalent) metallic element; brittle at low temperatures but liquid above room temperature; occurs in trace amounts in bauxite and zinc ores

Also: atomic number 31.

Not playable in Scrabble US: GA.