Basalt is a hard, dark rock, green-black to black when it is fresh, that comes from lava. When volcanoes pour out runny lava, it often cools into basalt. A huge amount of the ocean floor is made of it; so are places like Hawaii and many old lava fields. Up close it looks fine-grained, not sparkly like granite. In the weather it can turn brown or grey on the outside, so a road-cut may look dull until you break a piece and see the dark inside. People use it for paving and building because it is tough. It is a science-class and geography word, not a kitchen word. The spelling -salt is an accident of an old Latin name; it has nothing to do with table salt. The old story of the name, if you want it, is a bit crooked: Late Latin wrote basaltes, which was a misspelling of Latin basanites, from a Greek word for a touchstone, and that Greek word probably came from an Egyptian name for a hard stone.