The Collaborative International Dictionary of English v.0.48:

Whinstone \Whin"stone"\, n. [Whin + stone; cf. Scot.
   quhynstane.]
   A provincial name given in England to basaltic rocks, and
   applied by miners to other kind of dark-colored unstratified
   rocks which resist the point of the pick. -- for example, to
   masses of chert. Whin-dikes, and whin-sills, are names
   sometimes given to veins or beds of basalt.
   [1913 Webster]

WordNet (r) 3.0 (2006):

whinstone
    n 1: any of various hard colored rocks (especially rocks
         consisting of chert or basalt) [syn: whinstone, whin]