Rocks and Minerals Easier - Rocks are hard natural materials of mineral origin. Different kinds of rocks make up the crust of our planet Earth. Harder - A rock is defined as an aggregate of mineral grains, which means that rocks are a bunch of mineral grains all stuck together. The three types of rocks are igneous, sedimentary and metamorphic.
Igneous rocks form when molten rock, or magma, cools and hardens.
Sedimentary rocks result from erosion of any rock type, followed by depositing the resulting sediment into a natural basin, and finally cementing the sediment into stone. Metamorphic rocks form when any rock is subjected to great heat and pressure, but not enough heat to melt the rock. This site is a great starting point for kids of all ages who collect rocks, minerals and fossils. The rock cycle is a group of changes. Igneous rock can change into sedimentary or metamorphic rocks.