Specializing in the scientific study of the

Transmitted light[edit]
When light passes from air or a vacuum into a transparent crystal, some of it is reflected at the surface and some refracted. The latter is a bending of the light path that occurs because the speed of light changes as it goes into the crystal; Snell's law relates the bending angle to the Refractive index, the ratio of speed in a vacuum to speed in the crystal. Crystals whose point symmetry group falls in the cubic system are isotropic: the index does not depend on direction. All other crystals are anisotropic: light passing through them is broken up into two plane polarized rays that travel at different speeds and refract at different angles.^{[9]: 289–291}
A polarizing microscope is similar to an ordinary microscope, but it has two plane-polarized filters, a (polarizer) below the sample and an analyzer above it, polarized perpendicular to each other. Light passes successively through the polarizer, the sample and the analyzer. If there is no sample, the analyzer blocks all the light from the polarizer. However, an anisotropic sample will generally change the polarization so some of the light can pass through. Thin sections and powders can be used as samples.^{[9]: 293–294}
When an isotropic crystal is viewed, it appears dark because it does not change the polarization of the light. However, when it is immersed in a calibrated liquid with a lower index of refraction and the microscope is thrown out of focus, a bright line called a Becke line appears around the perimeter of the crystal. By observing the presence or absence of such lines in liquids with different indices, the index of the crystal can be estimated, usually to within ± 0.003.^{[9]: 294–295}
Systematic[edit]

Hanksite, Na₂₂K(SO₄)₉(CO₃)₂Cl, one of the few minerals that is considered a carbonate and a sulfate
See also: Mineral § Mineral classes
Systematic mineralogy is the identification and classification of minerals by their properties. Historically, mineralogy was heavily concerned with taxonomy of the rock-forming minerals. In 1959, the International Mineralogical Association formed the Commission of New Minerals and Mineral Names to rationalize the nomenclature and regulate the introduction of new names. In July 2006, it was merged with the Commission on Classification of Minerals to form the Commission on New Minerals, Nomenclature, and Classification.^[13] There are over 6,000 named and unnamed minerals, and about 100 are discovered each year.^[14] The Manual of Mineralogy places minerals in the following classes: native elements, sulfides, sulfosalts, oxides and hydroxides, halides, carbonates, nitrates and borates, sulfates, chromates, molybdates and tungstates, phosphates, arsenates and vanadates, and silicates.^[9]
Formation environments[edit]
The environments of mineral formation and growth are highly varied, ranging from slow crystallization at the high temperatures and pressures of igneous melts deep within the Earth's crust to the low temperature precipitation from a saline brine at the Earth's surface.
Various possible methods of formation include:^[15]

• 
  sublimation from volcanic gases
  
• 
  deposition from aqueous solutions and hydrothermal brines
  
• 
  crystallization from an igneous magma or lava
  
• 
  recrystallization due to metamorphic processes and metasomatism
  
• 
  crystallization during diagenesis of sediments
  
• 
  formation by oxidation and weathering of rocks exposed to the atmosphere or within the soil environment.
  

Biomineralogy[edit]
Biomineralogy is a cross-over field between mineralogy, paleontology and biology. It is the study of how plants and animals stabilize minerals under biological control, and the sequencing of mineral replacement of those minerals after deposition.^[16] It uses techniques from chemical mineralogy, especially isotopic studies, to determine such things as growth forms in living plants and animals^[17][18] as well as things like the original mineral content of fossils.^[19]
A new approach to mineralogy called mineral evolution explores the co-evolution of the geosphere and biosphere, including the role of minerals in the origin of life and processes as mineral-catalyzed organic synthesis and the selective adsorption of organic molecules on mineral surfaces.^[20][21]
Mineral ecology[edit]
In 2011, several researchers began to develop a Mineral Evolution Database.^[22] This database integrates the crowd-sourced site Mindat.org, which has over 690,000 mineral-locality pairs, with the official IMA list of approved minerals and age data from geological publications.^[23]
This database makes it possible to apply statistics to answer new questions, an approach that has been called mineral ecology. One such question is how much of mineral evolution is deterministic and how much the result of chance. Some factors are deterministic, such as the chemical nature of a mineral and conditions for its stability; but mineralogy can also be affected by the processes that determine a planet's composition. In a 2015 paper, Robert Hazen and others analyzed the number of minerals involving each element as a function of its abundance. They found that Earth, with over 4800 known minerals and 72 elements, has a power law relationship. The Moon, with only 63 minerals and 24 elements (based on a much smaller sample) has essentially the same relationship. This implies that, given the chemical composition of the planet, one could predict the more common minerals. However, the distribution has a long tail, with 34% of the minerals having been found at only one or two locations. The model predicts that thousands more mineral species may await discovery or have formed and then been lost to erosion, burial or other processes. This implies a role of chance in the formation of rare minerals occur.^{[24][25][26][27]}
In another use of big data sets, network theory was applied to a dataset of carbon minerals, revealing new patterns in their diversity and distribution. The analysis can show which minerals tend to coexist and what conditions (geological, physical, chemical and biological) are associated with them. This information can be used to predict where to look for new deposits and even new mineral species.^[28][29][30]

A color chart of some raw forms of commercially valuable metals.^[31]
Uses[edit]
Minerals are essential to various needs within human society, such as minerals used as ores for essential components of metal products used in various commodities and machinery, essential components to building materials such as limestone, marble, granite, gravel, glass, plaster, cement, etc.^[15] Minerals are also used in fertilizers to enrich the growth of agricultural crops.

A small collection of mineral samples, with cases. Labels in Russian.
Collecting[edit]
Mineral collecting is also a recreational study and collection hobby, with clubs and societies representing the field.^[32][33] Museums, such as the Smithsonian National Museum of Natural History Hall of Geology, Gems, and Minerals, the Natural History Museum of Los Angeles County, the Carnegie Museum of Natural History, the Natural History Museum, London, and the private Mim Mineral Museum in Beirut, Lebanon,^[34][35] have popular collections of mineral specimens on permanent display