Yes, GUINEA is a Scrabble word!

Letter values in Scrabble US: G 2, U 1, I 1, N 1, E 1, A 1.

Is it a valid word?

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

a former British gold coin worth 21 shillings
(ethnic slur) offensive term for a person of Italian descent
a republic in western Africa on the Atlantic; formerly a French colony; achieved independence from France in 1958
a west African bird having dark plumage mottled with white; native to Africa but raised for food in many parts of the world

Also: republic of guinea, french guinea, guinea fowl, numida meleagris.