The Collaborative International Dictionary of English v.0.48:
breakstone \break"stone`\ n. 1. Any of various plants of the genus Saxifraga. Syn: saxifrage, rockfoil. [WordNet 1.5]WordNet (r) 3.0 (2006):
breakstone n 1: any of various plants of the genus Saxifraga [syn: saxifrage, breakstone, rockfoil]