The Collaborative International Dictionary of English v.0.48:
Jackstone \Jack"stone`\, n.
1. One of the pebbles or pieces used in the game of
jackstones.
[1913 Webster]
2. (pl.) A game played with five small stones or pieces of
metal. See 6th Chuck. Also called jacks. See
jack[12], n.
[1913 Webster]