The earth is a rocky planet, made up of many different types of rock that have undergone different geological processes throughout time. Rocks can be classified into three main categories based on how they were formed: sedimentary, igneous and metamorphic.
Rocks are chemically made up of different minerals, which are inorganic substances found within the earth that have a crystalline structure. Minerals are made up of different elements that have formed compounds, with certain elements being very abundant in the earth's crust. The most abundant element in the earth's crust is oxygen, found within rocks in a variety of compounds such as carbonates (CO3), sulfates (SO4) and phosphates (PO4).
Metals such as aluminum and iron are also found widely throughout the earth's crust within various compounds. For example, pyrite, or fool's gold, is an iron ore in which iron is in a compound with sulfur (FeS2). Salts are another common example of minerals found in the earth. Rock salt (NaCl) is a compound occurring naturally, containing sodium(Na) and chlorine (Cl).
