Earliest use of obsidian

Obsidian is a rock formed when felsic lava from a volcanic eruption cools very quickly. The resulting rock is technically a type of naturally occurring glass, rather than a mineral, as the rapid cooling prevents the growth of crystals within its structure. The presence of magnesium and iron give obsidian its characteristic dark-brown-to-black colour. The sharp edges produced when obsidian is worked made it an invaluable resource to early humans, who used it for various cutting purposes. The earliest known use of obsidian by humans comes the Kariandusi prehistoric site in Kenya, and dates to around 700,000 years to the Lower Palaeolithic.