In Australia, when someone mentions Bluestone, they are generally referring to basalt, which is used extensively by the City of Melbourne.
Basalt is a volcanic rock, and is fine-grained due to the rapid cooling of lava at the surface of the planet. Usually grey to black in colour, it can be porphyritic, containing larger crystals.
Most commonly basalt has been used in highway construction, railroads and tiling, and is a major component of asphalt. Favoured during the Victorian Gold Rush, many significant buildings in Melbourne were constructed from this product, and it is still used in many small lanes and pavements.
Bluestone is a very visually appealing and looks fantastic when utilised in paving, walling and cobbles.