Yes, LANTHANUM is a Scrabble word!

Letter values in Scrabble US: L 1, A 1, N 1, T 1, H 4, A 1, N 1, U 1, M 3.

Is it a valid word?

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

a white soft metallic element that tarnishes readily; occurs in rare earth minerals and is usually classified as a rare earth

Also: atomic number 57.