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Whitlockite is a mineral, an unusual form of calcium phosphate. Its formula is Ca9(MgFe)(PO4)6PO3OH.〔〔〔 It is a relatively rare mineral but is found in granitic pegmatites, phosphate rock deposits, guano caves and in chondrite meteorites.〔 It was first described in 1941 and named for Herbert Percy Whitlock (1868–1948), American mineralogist, Curator, American Museum of Natural History, New York City, NY, USA.〔 With regards to periodontal dentistry, magnesium whitlockite comprises one component of many of the inorganic content of calculus. It is found primarily in subgingival calculus (as opposed to supragingival calculus). It is also found more in posterior as opposed to anterior regions of the oral cavity. == Historical evolution of whitlockite as distinct minerals == Whitlockite is a member of the phosphate group of minerals with three distinct occurrences. For many years, these occurrences were thought to be identical. However, recent studies using x-ray and electron diffraction have been able to identify compositional differences that separate one type of whitlockite from another. There are two inorganic occurrences of whitlockite that differ chiefly by the presence or absence of hydrogen. This difference was not initially observed due to technical limitations, such as small crystal size. Although the identity of the “true” whitlockite is still debated, efforts are now being made to officially distinguish terrestrial whitlockite from its phase in meteorites as two distinct minerals. Whitlockite can also be found in different types of biological deposits. Organic instances of whitlockite are virtually identical in composition, but typically contain magnesium, which further distinguishes them from inorganic instances of this mineral. Magnesium whitlockite has been implicated in different disease states and is currently being studied for use in the fabrication of human prosthetics. The phosphate group is part of the largest class of minerals and consists of 763 known species. Of these, the most common phosphate mineral is apatite, which is frequently found as an accessory mineral in many types of rock, including igneous and metamorphic rocks. Apatite has also been found in hydrothermal veins and cavities or even Alpine-type veins associated with quartz. The most important varieties of apatite are represented by fluorapatite, hydroxyapatite, chlorapatite and carbonate-apatite 〔Deer, W.A., R.A. Howie and J. Zussman. (1992) An Introduction to the Rock-Forming Minerals, 2nd Edition. Prentice Hall, Harlow〕〔Klein C. and B. Dutrow (2008) Mineral Science, 23rd Edition. Wiley, Inc., New York〕 Because the composition of apatite varies, the term ‘apatite’ is often used to describe a variety of different phosphate minerals. Apatite are also commonly found in biologic systems, where they are a frequent component of structures such as bone. Whitlockite is a rare phosphate mineral often represented as a type of apatite. However, it differs considerably from most other phosphate minerals, including apatite, in its chemical composition and the molar proportions of these components. The first serious studies of the mineral whitlockite were launched in 1952 on terrestrial specimens from the Palermo pegmatite quarry near North Groton, New Hampshire. These specimens were initially used to describe the composition and structure of the mineral.〔Calvo, C., and R. Gopal. (1975) The Crystal Structure of Whitlockite from the Palermo Quarry. American Mineralogist, 60: 120-133.〕 A decade later, the Apollo landing missions returned an impressive array of lunar rocks as well as other kinds of meteoric material. This unique resource led to an unprecedented barrage of geologic studies designed to characterize and define the composition and structure of minerals in these specimens. Throughout all studies on whitlockite, it has been found that the two most common phosphate minerals occurring in lunar rocks were apatite and whitlockite, and that they usually occur together.〔Joliff B.L., (2006) Crystal chemistry of lunar merrillite and comparison to other meteoretic and planetary suites of whitlockite and merrillite. American Mineralogist 91, 1583-1595.〕 In the biologic literature, whitlockite and apatite are use interchangeably. Whitlockite is also associated so frequently with apatite in its biologic occurrences that it is frequent presumed to be apatite.〔Lagier R., and C.-A. Baud. (2003). Magnesium whitlockite, a calcium phosphate crystal of special interest in pathology. Pathol. Res. Pract. 199, 329-335.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「whitlockite」の詳細全文を読む スポンサード リンク
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