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Article: Mineral


Definition and Classification of Minerals

  • A mineral is a solid substance with a specific chemical composition and crystal structure.
  • Minerals occur naturally in pure form and are distinct from rocks.
  • Some minerals can be biogenic or organic compounds.
  • Mineraloids are natural solid substances without a definite crystalline structure.
  • Different crystal structures of the same chemical compound are considered different mineral species.
  • The International Mineralogical Association (IMA) is the standard body for mineral species definition and nomenclature.
  • The IMA recognizes 5,955 official mineral species as of July 2023.
  • Small amounts of impurities can vary the chemical composition of a named mineral species.
  • Specific varieties of a mineral species may have their own names.
  • Minerals with variable proportions of chemical elements may form mineral groups.
  • To be considered a distinct mineral, it must occur naturally through geological processes.
  • Minerals must be solid in their natural occurrence, except for native mercury.
  • A mineral must have a well-defined crystallographic structure.
  • It must have a fairly well-defined chemical composition, although some substances with variable composition may be considered single mineral species.
  • Stability, crystal size, and controversies regarding amorphous substances are factors considered by the IMA.
  • Mineral species are commonly named after a person or discovery location.
  • Some mineral names are based on chemical composition or physical properties.
  • Most mineral names end in -ite, with exceptions for well-established names like galena and diamond.
  • The IMA has approved 5,955 mineral species.
  • Names based on chemical composition or physical properties are common in mineral naming.
  • The IMA excludes biogenic crystalline substances from the definition of minerals.
  • Some geologists and mineralogists argue that organisms can form minerals that cannot be formed inorganically.
  • Biominerals, created through metabolic activities of organisms, are considered minerals by some.
  • Advances in genetics and spectroscopy may provide new insights into the relationship between microorganisms and minerals.
  • The Working Group on Environmental Mineralogy and Geochemistry focuses on the biogeochemical aspects of minerals.

Minerals in Different Environments

  • Minerals can be found on nearly every rock, soil, and particle surface.
  • They exist in the hydrosphere, atmosphere, and biosphere.
  • Microorganisms contribute to the formation of minerals through biogeochemical cycles.
  • These microorganisms can precipitate metals from solution, forming ore deposits.
  • They can also catalyze the dissolution of minerals.

Rocks, Ores, and Gems

  • Schist is a metamorphic rock characterized by platy minerals.
  • Rocks are aggregates of one or more minerals.
  • Some rocks are primarily composed of one mineral, such as limestone or quartzite.
  • Granite is defined by proportions of quartz, alkali feldspar, and plagioclase feldspar.
  • The major rock-forming minerals include quartz, feldspars, micas, amphiboles, pyroxenes, olivines, and calcite.
  • Commercially valuable minerals other than gemstones, metal ores, or mineral fuels are known as industrial minerals.
  • Muscovite, a white mica, can be used for windows, as a filler, or as an insulator.
  • Ores are minerals with a high concentration of a certain element, typically a metal.
  • Examples of ores include cinnabar, sphalerite, cassiterite, and colemanite.
  • Gems are minerals with ornamental value, distinguished by their beauty, durability, and rarity.

Crystal Structure and Chemical Composition

  • The abundance and diversity of minerals are controlled by their chemistry.
  • Eight elements, including oxygen and silicon, account for most of the key components of minerals.
  • The minerals that form are those that are most stable at the temperature and pressure of formation.
  • Complex thermodynamic calculations are required to predict the minerals present in a rock of a particular composition.
  • Chemical substitution and coordination polyhedra explain the variability in mineral composition.
  • Coordination polyhedra are geometric representations of how a cation is surrounded by an anion.
  • The base unit of silicate minerals is the silica tetrahedron, with one Si surrounded by four O.
  • Silicon typically has a coordination number of 4, except in high-pressure minerals where it is in six-fold coordination with oxygen.
  • The substitution of Si by Al allows for a variety of minerals due to the need to balance charges.
  • Bigger cations have bigger coordination numbers compared to oxygen.
  • Aluminosilicates like kyanite, andalusite, and sillimanite differ in the coordination number of Al.
  • Changes in pressure and temperature can cause these minerals to transition from one another.
  • Changes in temperature, pressure, and composition can alter the mineralogy of a rock sample.
  • Changes in composition can be caused by processes like weathering or hydrothermal alteration.
  • Changes in temperature and pressure occur during tectonic or magmatic movement.
  • Thermodynamic conditions can lead to mineral reactions and the formation of new minerals.
  • Two rocks can have similar bulk rock chemistry but different mineralogy due to mineralogical alteration.

Physical Properties and Crystal Habit

  • Classifying minerals involves considering physical properties.
  • Physical properties used for classification include crystal structure, hardness, lustre, color, and specific gravity.
  • Other tests like fluorescence, magnetism, and reactivity to acids can also be used.
  • Optical, chemical, or X-ray diffraction analysis may be required for complex identification.
  • Some physical properties are sufficient for full identification, while others require more detailed analysis.
  • Crystal structure is based on the orderly arrangement of atoms in a mineral's internal structure.
  • Crystal structure can be determined by X-ray diffraction.
  • Minerals are described by their symmetry content and belong to 32 point groups.
  • Polymorphs are minerals with the same chemical formula but different crystal structures.
  • Differences in crystal structure and chemistry influence other physical properties of minerals.
  • Various types of twins exist, including contact twins, reticulated twins, geniculated

Mineral Data Sources

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