Traditionally, inorganic compounds are considered to be of a mineral, not biological origin. Complementarily, most organic compounds are traditionally viewed as being of biological origin. Over the past century, the precise classification of inorganic vs organic compounds has become less important to scientists, primarily because the majority of known compounds are synthetic and not of natural origin. Furthermore, most compounds considered the purview of modern inorganic chemistry contain organic ligands. The fields of organometallic chemistry and bioinorganic chemistry explicitly focus on the areas between the fields of organic, biological, and inorganic chemistry.
Inorganic compounds can be formally defined with reference to what they are not—organic compounds. Organic compounds contain carbon bonds in which at least one carbon atom is covalently linked to an atom of another type (commonly hydrogen, oxygen or nitrogen). Some carbon-containing compounds are traditionally considered inorganic *. When considering inorganic chemistry and life, it is useful to recall that many species in nature are not compounds per se, but are ions. Sodium, chloride, and phosphate ions are essential for life, as are some inorganic molecules such as carbonic acid, nitrogen, carbon dioxide, water and oxygen. Aside from these simple ions and molecules, virtually all compounds covered by bioinorganic chemistry contain carbon and can be considered organic or organometallic.
Inorganic carbon compounds
Many compounds that contain carbon are considered inorganic; for example, carbon monoxide, carbon dioxide, carbonates, cyanides, cyanates, carbides, and thyocyanates. In general, however, the workers in these areas are not concerned about strict definitions.
A large class of compounds discussed in inorganic chemistry textbooks are coordination compounds. Examples range from substances that are strictly inorganic, such as [Co(NH3)6]Cl3, to organometallic compounds such as Fe(C5H5)2 and extending to bioinorganic compounds, such as the hydrogenase enzymes.
Minerals are mainly oxides and sulfides, which are strictly inorganic. In fact, most of the earth and the universe is inorganic. Although the components of the Earth's crust are well elucidated, the processes of mineralization and the composition of the deep mantle remain active areas of investigation, which are mainly covered in geology-oriented venues.