Yes, MANTLE is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, N 1, T 1, L 1, E 1.

Is it a valid word?

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

the cloak as a symbol of authority
United States baseball player (1931-1997)
the layer of the earth between the crust and the core
anything that covers
(zoology) a protective layer of epidermis in mollusks or brachiopods that secretes a substance forming the shell
shelf that projects from wall above fireplace
hanging cloth used as a blind (especially for a window)
a sleeveless garment like a cloak but shorter

Also: mickey mantle, mickey charles mantle.

Not playable in Scrabble US: MANTLEPIECE.