Bluestone
Technical Bluestone Information
In Australia when people speak of Bluestone they are generally referring to Basalt, which is used extensively by the City of Melbourne.
Basalt is a common extrusive volcanic rock. It is usually gray to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or gray.
The most common uses for this rock are as aggregate in highway construction, railroad ballast, and tile. Basalt is also a major component of asphalt.
On Earth, most basalt magmas have formed by decompression melting of the mantle. Basalt has also formed on Earth's Moon, Mars, Venus, and even on the asteroid Vesta. Source rocks for the partial melts probably include both peridotite and pyroxenite. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below ocean ridges. [ Source ]