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