What is Basalt?
When the lava cools quickly, it turns into basalt. Usually basalt is black or gray. Basalt is a mixture of feldspar and pyroxene, a rock made mainly of silica and oxygen. Pyroxene is what jade is before metamorphosis.
Asphalt pavement made with basalt
Like granite, basalt is a very hard rock. Because it is a common rock and so hard, people used basalt for early choppers and for grinding stones for grinding grains like millet and barley. Roman engineers paved a lot of Roman roads with basalt, and today engineers still use a lot of ground-up basalt to make asphalt to pave roads.