Molten rock, or magma, contains the chemical elements that form silicate minerals. Once these elements begin to form chemical bonds within the magma, crystals start to develop. Seventy percent of the Earth's surface is basalt, with most of it found on the ocean floors. Other silicate minerals, such as potassium feldspar and quartz, crystallize at lower temperatures. These minerals are the primary constituents of granitic rocks.
Granite is the rock that makes up the majority of the continental crust.