Yes, JACKSTONES is a Scrabble word!

Letter values in Scrabble US: J 8, A 1, C 3, K 5, S 1, T 1, O 1, N 1, E 1, S 1.

Is it a valid word?

JACKSTONES is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

game equipment consisting of one of several small six-pointed metal pieces that are picked up while bouncing a ball in the game of jacks
a game in which jackstones are thrown and picked up in various groups between bounces of a small rubber ball