Whitlockite

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Whitlockite
pyroelectric
References[2][3][4]

Whitlockite is a mineral, an unusual form of

phosphate rock deposits, guano caves and in chondrite meteorites.[4] It was first described in 1941 and named for Herbert Percy Whitlock (1868–1948), American mineralogist and curator at the American Museum of Natural History in New York City.[3]

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 as distinct minerals

Whitlockite is a member of the

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[5] 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

chlorapatite and carbonate-apatite
[6][7] 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.[8] 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.[9] 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 frequently presumed to be apatite.[5]

Bobdownsite is a variety of whitlockite from

Yukon, Canada, that was thought to contain fluorine bonded directly to phosphorus, giving it the chemical formula Ca9(Mg)(PO4)6(PO3F)[10] However, subsequent investigation failed to find any monofluorophosphate in samples of bobdownsite, the mineral was discredited as a distinct species, and recommendations were made to tighten the criteria for identifying minerals as containing monofluorophosphate.[11]

Geological occurrences

Whitlockite has two

martian and other types of meteorites, where it is one of the most common phosphate minerals. Studies of merrillite as an accessory mineral have provided valuable insights that have helped to unlock the petrogenesis of extraterrestrial rocks.[13]

Biological occurrences

Whitlockite can also be found in biological systems and has been implicated in several human diseases.

cations in biologic fluids. Formation of this type of whitlockite is magnesium rich, and is preferred at temperatures typical of biologic systems because of the smaller diameter of the magnesium ion compared to calcium.[5]

Physical properties

Each of the phases of whitlockite described above exhibit approximately the same physical properties. They display no

rhombohedral crystals, but whitlockite can also rarely be tabular. The crystal habit of whitlockite also ranges from coarse granular to earthy.[15]

See also

References

  1. S2CID 235729616
    .
  2. ^ a b Whitlockite: Whitlockite mineral data from Mindat
  3. ^ a b c Whitlockite Mineral Data from Webmineral
  4. ^ a b c http://rruff.geo.arizona.edu/doclib/hom/whitlockite.pdf Handbook of Mineralogy
  5. ^
    PMID 12908523
    .
  6. ^ Deer, W.A., R.A. Howie and J. Zussman. (1992) An Introduction to the Rock-Forming Minerals, 2nd Edition. Prentice Hall, Harlow
  7. ^ Klein C. and B. Dutrow (2008) Mineral Science, 23rd Edition. Wiley, Inc., New York
  8. ^ Calvo, C., and R. Gopal. (1975) The Crystal Structure of Whitlockite from the Palermo Quarry. American Mineralogist, 60: 120-133.
  9. ^ 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.
  10. ^ Tait, Kimberly T.,Madison C. Barkley, Richard M. Thompson, Marcus J. Origlieri, Stanley H. Evans, Charles T. Prewitt, and Hexiong Yang, "Bobdownsite, A New Mineral Species From Big Fish River, Yukon, Canada, and Its Structural Relationship With Whitlockite-Type Compounds", The Canadian Mineralogist, 49.4 (2011): (1065-1078). Print.
  11. S2CID 53580850
    .
  12. ^ Roberts et al. 1974
  13. ^ Jolliff, et al., 2006
  14. ^ Lee, R.S., M.V. Kayser . S.Y. Ali (2006) Calcium phosphate microcrystal deposition in the human intervertebral disc. J. Anat. 208, 13-9
  15. ^ Hughes, J.M., Jolliff, B.L. and M.E. Gunter. (2006). The atomic arrangement of merrillite from the Fra Mauro Formation, Appllol 143 lunar mission: The first structure of merrillite from the Moon. American Mineralogist, 91, 1547-1552
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