In geology, minerals are defined as inorganic solids produced by geological processes with a regular crystal structure and a defined chemical composition. Typically, substances such as coal, pearls, opal, or obsidian that do not meet the definition are called mineraloids. Minerals are formed when atoms are bonded together in a crystalline arrangement. There are three main ways of mineral formation in nature, namely, direct precipitation from water solutions with temperature change, crystallization from magma with temperature change, and biological precipitation by the action of organisms. A rock is a substance that contains one or more minerals or mineraloids. Rocks can be classified into igneous, sedimentary, and metamorphic rocks according to their formation. Igneous rocks are formed from the cooling and solidification of magma, which can be divided into felsic, intermediate, mafic, and ultramafic based on their chemical composition. Sedimentary rocks are formed from deposits of preexisting rocks or fragments of once living organisms. When the sediments are buried deeply, they are compacted and cemented by the pressure to form sedimentary rocks such as sandstone, shale, or limestone. Metamorphic rocks are rocks that have become changed from their original form by intense heat or pressure while forming, and common metamorphic rocks are phyllite, schist, gneiss, quartzite, and marble.
Minerals can be divided into silicates and non-silicates. Silicate minerals, which are built around silico-oxygen tetrahedrons, constitute the largest group of minerals on Earth and make up the vast majority of the Earth's mantle and crust. Silicate minerals include quartz, feldspar, mica, olivine, etc. Quartz and feldspar are the two most abundant minerals in the continental crust, belonging to felsic minerals. Felsic refers to silicate minerals, magma, and igneous rocks which contain an abundance of the lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. Mafic minerals are silicate minerals or igneous rocks rich in magnesium and iron. Common mafic minerals include olivine, pyroxene, amphibole, and biotite. Mafic silicates tend to be denser than non-mafic silicates. Although most of the Earth's crust is made up of silicate minerals, non-silicate minerals are of great importance. The most common non-silicates are carbonates, oxides, and sulfides. Many important metal ores are sulfides, in which the metal is combined with sulfur, such as galena (lead sulfide), sphalerite (zinc sulfide), pyrite (iron sulfide), and chalcopyrite (iron-copper sulfide). Galena is the main source of lead and sphalerite is the main source of zinc. In addition, the largest sources of nickel, antimony, molybdenum, arsenic and mercury are also sulfides.
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