Granite is an igneous rock containing principally quartz, alkali and plagioclase feldspar. It is an acid rock, meaning that it formed on the continental plates. It tends to lack internal structures, such as faults, and is extremely hard-wearing. Granites range in colour from pink to grey. Due to their hardness, colouring and the consistency of their texture granites were popular in the Roman world for monolithic columns but also some sculpture, large basins and panels for revetment and flooring. The main sources of granite targeted in the Roman period were in Egypt, in the Eastern Desert and at Aswan on the Nile, in the Troad in Turkey, and around the Tyrrhenian Sea, especially on Elba, Giglio, Corsica and Sardinia. Granite is carved in a quite different manner from other stones, with the tools held closer to vertical during carving. Fragile tools, like the tooth chisel, are not used for granite carving.