A mineral is defined as naturally occurring solid, that is stable at room temperature, represent able by a chemical formula, usually a biogenic (not resulting from the activity of living organisms), and has an ordered atomic structure.  Minerals are not equivalent to rocks. A rock is either an aggregate of one or more minerals, or not composed of minerals at all.  Coal is a sedimentary rock composed primarily of organically derived carbon.

Two common classifications are used for minerals; both the Dana and Strunz classifications rely on the composition of the mineral, specifically with regards to important chemical groups, and its structure. The Dana System of Mineralogy was first published in 1837 by James Dwight Dana, a leading geologist of his time; it is presently in its eighth edition (1997 ed.). The Dana classification, assigns a four-part number to a mineral species. First is its class, based on important compositional groups; next, the type gives the ratio of cations to anions in the mineral; finally, the last two numbers group minerals by structural similarity with a given type or class. The less commonly used Strunz classification, named for German mineralogist Karl Hugo Strunz, is based on the Dana system, but combines both chemical and structural criteria, the latter with regards to distribution of chemical bonds.

There are over 4,900 known mineral species; over 4,660 of these have been approved by the International Mineralogical Association (IMA). The silicate minerals compose over 90% of the Earth’s crust. The diversity and abundance of mineral species is controlled by the Earth’s chemistry. Silicon and oxygen constitute approximately 75% of the Earth’s crust, which translates directly into the predominance of silicate minerals. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish various species, and these properties in turn are influenced by the mineral’s geological environment of formation. 

Click on an image below to see a larger version: