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