Science and Technology for UPSC Examinations [Chemistry] Part 12- Basics of Minerals and Ores
A mineral is a naturally occurring substance that is solid and stable at room temperature, representable by a chemical formula, usually abiogenic, and has an ordered atomic structure. It is different from a rock, which can be an aggregate of minerals or non-minerals, and does not have a specific chemical composition. There are around 5000 known minerals. 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.
The general definition of a mineral encompasses the following criteria:
- Naturally occurring
- Stable at room temperature
- Represented by a chemical formula
- Usually abiogenic
- Ordered atomic arrangement
As the composition of the Earth’s crust is dominated by silicon and oxygen, silicate elements are by far the most important class of minerals in terms of rock formation and diversity. However, non-silicate minerals are of great economic importance, especially as ores. Non-silicate minerals are subdivided into several other classes by their dominant chemistry, which included native elements, Sulfides, halides, oxides and hydroxides, carbonates and nitrates, borates, sulphates, phosphates, and organic compounds. The majority of non-silicate mineral species are extremely rare (constituting in total 8% of the Earth’s crust), although some are relative common, such as calcite, pyrite, magnetite, and hematite.
Minerals versus Ores
The Inorganic elements or compounds of various metals found in nature, associated with their earthly impurities are called Minerals. For example, sodium chloride – NaCl, potassium chloride – KCl, calcium carbonate, – CaCO3, magnesium carbonate – MgCO3, zinc sulphide – ZnS, cuprous sulphide – Cu2S etc., which are found in nature are minerals. Some minerals may contain a large percentage of metals whereas others may contain only a small percentage. All the minerals cannot be used to extract metals. Those minerals from which metals can be extracted profitably and conveniently are called Ores.
There are four types of Ores
- Oxide ores : Bauxite Al2O3 . 2H2O, Cuprite Cu2O, Zincite ZnO, Haematite Fe2O3, Pyrolusite MnO2
- Sulphide ores : Copper pyrites CuFeS2, Argentite Ag2S, Zinc blende ZnS, Cinnabar HgS, Galena PbS and Copper glance Cu2S.
- Carbonate ores : Limestone CaCO3, Calamine ZnCO3.
- Halide ores : Rock salt NaCl, Fluorspar CaF2