The Collaborative International Dictionary of English v.0.48:

Bluestone \Blue"stone`\, n.
   1. Blue vitriol. --Dunglison.
      [1913 Webster]

   2. A grayish blue building stone, as that commonly used in
      the eastern United States.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bluestone
    n 1: bluish-grey sandstone used for paving and building