Mineralogy is a subject ofgeology specializing in the scientific study of thechemistry,crystal structure, and physical (includingoptical) properties ofminerals and mineralizedartifacts. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, and their utilization.
Early writing on mineralogy, especially ongemstones, comes from ancientBabylonia, the ancientGreco-Roman world, ancient and medievalChina, andSanskrit texts fromancient India and the ancient Islamic world.[2] Books on the subject included theNatural History ofPliny the Elder, which not only described many different minerals but also explained many of their properties, and Kitab al Jawahir (Book of Precious Stones) by Persian scientistAl-Biruni. TheGerman Renaissance specialistGeorgius Agricola wrote works such asDe re metallica (On Metals, 1556) andDe Natura Fossilium (On the Nature of Rocks, 1546) which began the scientific approach to the subject. Systematic scientific studies of minerals and rocks developed in post-Renaissance Europe.[2] The modern study of mineralogy was founded on the principles ofcrystallography (the origins of geometric crystallography, itself, can be traced back to the mineralogy practiced in the eighteenth and nineteenth centuries) and to themicroscopic study of rock sections with the invention of themicroscope in the 17th century.[2]
Nicholas Steno first observed thelaw of constancy of interfacial angles (also known as the first law of crystallography) in quartz crystals in 1669.[3]: 4 This was later generalized and established experimentally byJean-Baptiste L. Romé de l'Islee in 1783.[4]René Just Haüy, the "father of modern crystallography", showed that crystals are periodic and established that the orientations of crystal faces can be expressed in terms of rational numbers (law of rational indices), as later encoded in the Miller indices.[3]: 4 In 1814,Jöns Jacob Berzelius introduced a classification of minerals based on their chemistry rather than their crystal structure.[5]William Nicol developed theNicol prism, which polarizes light, in 1827–1828 while studying fossilized wood;Henry Clifton Sorby showed that thin sections of minerals could be identified by their optical properties using apolarizing microscope.[3]: 4 [5]: 15 James D. Dana published his first edition ofA System of Mineralogy in 1837, and in a later edition introduced a chemical classification that is still the standard.[3]: 4 [5]: 15 X-ray diffraction was demonstrated byMax von Laue in 1912, and developed into a tool for analyzing the crystal structure of minerals by the father/son team ofWilliam Henry Bragg andWilliam Lawrence Bragg.[3]: 4
More recently, driven by advances in experimental technique (such asneutron diffraction) and available computational power, the latter of which has enabled extremely accurate atomic-scale simulations of the behaviour of crystals, the science has branched out to consider more general problems in the fields ofinorganic chemistry andsolid-state physics. It, however, retains a focus on the crystal structures commonly encountered in rock-forming minerals (such as theperovskites,clay minerals, andframework silicates). In particular, the field has made great advances in the understanding of the relationship between the atomic-scale structure of minerals and their function; in nature, prominent examples would be accurate measurement and prediction of the elastic properties of minerals, which has led to new insight intoseismological behaviour of rocks and depth-related discontinuities in seismograms of theEarth's mantle. To this end, in their focus on the connection between atomic-scale phenomena and macroscopic properties, themineral sciences (as they are now commonly known) display perhaps more of an overlap withmaterials science than any other discipline.
Hardness is determined by comparison with other minerals. In theMohs scale, a standard set of minerals is numbered in order of increasing hardness from 1 (talc) to 10 (diamond). A harder mineral will scratch a softer one, so an unknown mineral can be placed in this scale, by which minerals; it scratches and which scratch it. A few minerals, such ascalcite andkyanite have a hardness that depends significantly on direction.[7]: 254–255 Hardness can also be measured on an absolute scale using asclerometer; compared to the absolute scale, the Mohs scale is nonlinear.[6]: 52
Tenacity refers to the way a mineral behaves when it is broken, crushed, bent or torn. A mineral can bebrittle,malleable,sectile,ductile,flexible orelastic. An important influence on tenacity is the type of chemical bond (e.g.,ionic ormetallic).[7]: 255–256
Of the other measures of mechanical cohesion,cleavage is the tendency to break along certain crystallographic planes. It is described by the quality (e.g., perfect or fair) and the orientation of the plane in crystallographic nomenclature.
Parting is the tendency to break along planes of weakness due to pressure, twinning orexsolution. Where these two kinds of break do not occur,fracture is a less orderly form that may beconchoidal (having smooth curves resembling the interior of a shell),fibrous,splintery,hackly (jagged with sharp edges), oruneven.[7]: 253–254
If the mineral is well crystallized, it will also have a distinctivecrystal habit (for example, hexagonal, columnar,botryoidal) that reflects thecrystal structure or internal arrangement of atoms.[6]: 40–41 It is also affected by crystal defects andtwinning. Many crystals arepolymorphic, having more than one possible crystal structure depending on factors such as pressure and temperature.[3]: 66–68 [6]: 126
Theperovskite crystal structure. The most abundant mineral in the Earth,bridgmanite, has this structure.[8] Its chemical formula is (Mg,Fe)SiO3; the red spheres are oxygen, the blue spheres silicon and the green spheres magnesium or iron.
The crystal structure is the arrangement of atoms in a crystal. It is represented by alattice of points which repeats a basic pattern, called aunit cell, in three dimensions. The lattice can be characterized by its symmetries and by the dimensions of the unit cell. These dimensions are represented by threeMiller indices.[9]: 91–92 The lattice remains unchanged by certain symmetry operations about any given point in the lattice:reflection,rotation,inversion, androtary inversion, a combination of rotation and reflection. Together, they make up a mathematical object called acrystallographic point group orcrystal class. There are 32 possible crystal classes. In addition, there are operations that displace all the points:translation,screw axis, andglide plane. In combination with the point symmetries, they form 230 possiblespace groups.[9]: 125–126
Most geology departments haveX-raypowder diffraction equipment to analyze the crystal structures of minerals.[6]: 54–55 X-rays have wavelengths that are the same order of magnitude as the distances between atoms.Diffraction, the constructive and destructive interference between waves scattered at different atoms, leads to distinctive patterns of high and low intensity that depend on the geometry of the crystal. In a sample that is ground to a powder, the X-rays sample a random distribution of all crystal orientations.[10] Powder diffraction can distinguish between minerals that may appear the same in a hand sample, for examplequartz and its polymorphstridymite andcristobalite.[6]: 54
Since 1960, most chemistry analysis is done using instruments. One of these,atomic absorption spectroscopy, is similar to wet chemistry in that the sample must still be dissolved, but it is much faster and cheaper. The solution is vaporized and its absorption spectrum is measured in the visible and ultraviolet range.[7]: 225–226 Other techniques areX-ray fluorescence,electron microprobe analysisatom probe tomography andoptical emission spectrography.[7]: 227–232
In addition to macroscopic properties such as colour or lustre, minerals have properties that require a polarizing microscope to observe. Recently, the field of digital mineral study and identification has been developing based on the optical properties of minerals, including through the use of artificial intelligence technologies[11].
When light passes from air or avacuum into a transparent crystal, some of it isreflected at the surface and somerefracted. The latter is a bending of the light path that occurs because thespeed of light changes as it goes into the crystal;Snell's law relates the bendingangle to theRefractive index, the ratio of speed in a vacuum to speed in the crystal. Crystals whose point symmetry group falls in thecubic system areisotropic: the index does not depend on direction. All other crystals areanisotropic: light passing through them is broken up into two planepolarizedrays that travel at different speeds and refract at different angles.[7]: 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.[7]: 293–294
When an isotropic crystal is viewed, it appears dark because it does not change the polarization of the light. However, when it isimmersed in a calibrated liquid with a lower index of refraction and the microscope is thrown out of focus, a bright line called aBecke 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.[7]: 294–295
The environments of mineral formation and growth are highly varied, ranging from slow crystallization at the high temperatures and pressures ofigneousmelts deep within the Earth'scrust to the low temperature precipitation from a saline brine at the Earth's surface.
Various possible methods of formation include:[14]
Biomineralogy is a cross-over field between mineralogy,paleontology andbiology. 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.[15] It uses techniques from chemical mineralogy, especially isotopic studies, to determine such things as growth forms in living plants and animals[16][17] as well as things like the original mineral content of fossils.[18]
A new approach to mineralogy calledmineral 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.[19][20]
In 2011, several researchers began to develop a Mineral Evolution Database.[21] This database integrates thecrowd-sourced siteMindat.org, which has over 690,000 mineral-locality pairs, with the official IMA list of approved minerals and age data from geological publications.[22]
This database makes it possible to applystatistics to answer new questions, an approach that has been calledmineral ecology. One such question is how much of mineral evolution isdeterministic and how much the result ofchance. Some factors are deterministic, such as the chemical nature of a mineral and conditions for itsstability; 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 apower 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 along 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.[23][24][25][26]
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.[27][28][29]
A color chart of some raw forms of commercially valuable metals.[30]
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^"Law of the constancy of interfacial angles".Online dictionary of crystallography. International Union of Crystallography. 24 August 2014.Archived from the original on 19 October 2016. Retrieved22 September 2015.
^abcRafferty, John P. (2012).Geological sciences (1st ed.). New York: Britannica Educational Pub. in association with Rosen Educational Services. pp. 14–15.ISBN9781615304950.
^abcdefKlein, Cornelis; Philpotts, Anthony R. (2013).Earth materials : introduction to mineralogy and petrology. New York: Cambridge University Press.ISBN9780521145213.
^abcdefghijkKlein, Cornelis; Hurlbut, Cornelius S. Jr. (1993).Manual of mineralogy : (after James D. Dana) (21st ed.). New York: Wiley.ISBN047157452X.
^Dinnebier, Robert E.; Billinge, Simon J.L. (2008). "1. Principles of powder diffraction". In Dinnebier, Robert E.; Billinge, Simon J.L. (eds.).Powder diffraction : theory and practice (Repr. ed.). Cambridge: Royal Society of Chemistry. pp. 1–19.ISBN9780854042319.
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^Hazen, Robert M.; Grew, Edward S.; Downs, Robert T.; Golden, Joshua; Hystad, Grethe (March 2015). "Mineral ecology: Chance and necessity in the mineral diversity of terrestrial planets".The Canadian Mineralogist.53 (2):295–324.Bibcode:2015CaMin..53..295H.doi:10.3749/canmin.1400086.S2CID10969988.
^Hazen, Robert."Mineral Ecology".Carnegie Science.Archived from the original on 28 May 2018. Retrieved15 May 2018.
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