aggregate

Metalled road, Reinga, New Zealand.

Aggregate, in general, is mined, either as gravel or as stone which is then crushed to roughly 10mm sized pieces for concrete.  Historically this rock was called metal, from the Greek, metallon, or quarry/ore/metal, from which comes the term, a metalled road, something one finds in John Buchan novels where the hero and his invariably boyish girl companion hurtle across Scotland in their roadster on narrow tracks and if lucky, a metalled road.  Which merely means a gravel road.  The term is still used in New Zealand evidently.

Metalling is a process developed by John McAdam in 1820 where layers of ever-smaller sized aggregate are laid down on the road bed and with wear the sharp edges will pack together making a dense and weatherproof surface.  It is made even finer if the surface is coated with a mixture of stone dust and water, filling up any gaps between the stones.  Coating the lot with tar (tarmac) reduces dust as the surface stones break down with excessive wear.  

Asphalt is a name for bitumen, something we know a lot about here: originally called the tar sands of northern Alberta, the scientifically neutral term is the bitumen sands, the industry term is the oil sands: it is all heavy semi-solid petroleum.  Whatever, an asphalt concrete road which is what most of our roads are, is a gravel road topped with a layer of aggregate mixed with bitumen as the binder, rather than cement.

None of this is exotic, the basic materials seem to be everywhere, and evidently aggregate mining is what most of mining consists of.  There is a nasty history to rock breaking however, considered hard labour and done by prisoners well into the 20th century – including Nelson Mandela on Robben Island, and it is still done by women and children in the more benighted parts of the world.