Granite is an igneous rock, which means that at some time during its development, it was melted like volcanic lava. Unlike lava, however, this melted rock never reached the surface; it remained trapped inside the earth, where it slowly cooled and crystallized. The three main mineral components of this stone are feldspar, quartz and mica. The very hard and dense varieties of this stone are formed by tectonic shifts beneath the earth's crust. The closer to the surface the mass was when it hardened, the lower its density will be; these granites frequently have a lighter colour. A dark grey to black colour is a sign that the stone has hardened at a greater depth. A yellowish colour indicates iron oxidation close to the surface, with the stone having a low density. Granite is the hardest of all building stones with a very close grain, making it almost impervious to stain and uniquely applicable for any interior and exterior use.