Bluestone Co.

Bluestone is a cultural or commercial name for a number of natural dimension or building stone varieties, including:
It is unrelated to human-made blue brick.
The term "bluestone" in Britain is used in a loose sense to cover all of the "foreign," not intrinsic, stones and rock debris at Stonehenge. It is a "convenience" label rather than a geological term, since at least 46 different rock types are represented. One of the most common rocks in the assemblage is known... plus