To begin with, bluestone is not a geological term and does not fall within any distinct category such as igneous, sedimentary or metamorphic. Bluestone, in fact, represents in excess of 20 separate rock varieties.

In Australia, there are two varieties of bluestone, one is normally known as Victorian Bluestone which is a kind of basalt. Basalt is an igneous rock made up primarily of feldspar and is usually grey to black and fine-grained owing to the rapid cooling of lava at the surface of a planet. In South Australia, it is known as a type of slate. Slate is a metamorphic rock that is mostly made up of quartz and is typically pale grey or beige in color. It should be noted that it is a great deal less hard-wearing than the Victorian Bluestone.