Basalt is a fine-grained, hard rock that forms when bits of lava shoot out of volcanoes, so it's one kind of igneous rock. 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.
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