Yes, HOLMIUM is a Scrabble word!

Letter values in Scrabble US: H 4, O 1, L 1, M 3, I 1, U 1, M 3.

Is it a valid word?

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

a trivalent metallic element of the rare earth group; occurs together with yttrium; forms highly magnetic compounds

Also: atomic number 67.