Definition of bluestones:
(n) :
Any of several bluish-grey varieties of stone used for construction:
(n) :
(UK) A form of dolerite which appears blue when wet or freshly broken.
(n) :
(UK) Any of the several (massive) kinds of non-local stone (particularly dolerite) used to construct Stonehenge.
(n) :
(Australia, New Zealand) A bluish-grey basalt or olivine basalt.
(n) :
(US) A form of limestone found in the Shenandoah Valley and some other places.
(n) :
(US, Canada) A feldspathic sandstone found in the US and Canada.