General objective of this lecture is to present on types of Rocks. There are three main types of rocks: Igneous – formed when molten rock cools. These are rocks formed by the cooling of molten rock (magma). Sedimentary – formed by the “cementing together” of small grains of sediment. Sedimentary Rocks are rocks formed when particles of sediment build up and are “cemented together” by the effect of pressure and minerals. And Metamorphic – rocks changed by the effect of heat and pressure.