Yes, QUINTESSENCE is a Scrabble word!

Letter values in Scrabble US: Q 10, U 1, I 1, N 1, T 1, E 1, S 1, S 1, E 1, N 1, C 3, E 1.

Is it a valid word?

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

the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies
the purest and most concentrated essence of something
the most typical example or representative of a type