This is a lump of granite. Granite is a very hard, dense rock made from 3 main ingredients: mica, feldspar and quartz. Granite is an igneous rock.
Granite and other intrusive igneous rocks are formed when magma pushes up close to the earth's surface. The magma melts surrounding older rocks, combining with them as it does so. Then the whole mass slowly cools.
The large amount of quartz in granite makes it stand up well to weather and erosion. Because it is so dense and sturdy, granite is a good material for use in buildings, sculptures, roads and floors.