Whitlockite 3882845 215478603 2008-05-28T11:26:58Z Shiftchange 75349 /* Biologic occurrences */ add 1 wikilink to [[weight bearing]] {{Infobox mineral | name = Whitlockite | category = [[Phosphate]] Mineral | boxwidth = | boxbgcolor = | image = | imagesize = | caption = | formula = | molweight = 1,071.45 gm | color = Colorless, gray-white | habit = massive to tabular | system = Trigonal | twinning = | cleavage = None | fracture = Brittle | tenacity = Brittle | mohs = 5 | luster = Vitreous | polish = | refractive = | opticalprop = uniaxial (-) | birefringence = | dispersion = | pleochroism = | fluorescence= | absorption = | streak = White | gravity = | density = 3.13 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Transparent | other = | references =<ref>[http://www.mindat.org/min-4280.html Whitlockite: Whitlockite mineral information and data<!-- Bot generated title -->]</ref><ref>[http://www.webmineral.com/data/Whitlockite.shtml Whitlockite Mineral Data<!-- Bot generated title -->]</ref> }} '''Whitlockite''' is a mineral, an unusual form of [[Tricalcium phosphate|calcium phosphate]]. It's actual formula is debatable depending on the authority consulted; starting from [[calcium|Ca]]<sub>3</sub>([[phosphorus|P]][[oxygen|O]]<sub>4</sub>)<sub>2</sub> it may also contain [[magnesium]] (Ca[[magnesium|Mg]])<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub> to the more complex Ca<sub>9</sub>(Mg[[iron|Fe]])(PO<sub>4</sub>)<sub>6</sub>PO<sub>3</sub>O[[hydrogen|H]]. It is a relatively rare mineral but is found in [[granitic]] [[pegmatite]] and has also been found in [[meteorite]]s. 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 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. It comprises one component of many of the inorganic content of calculus. == 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 ecoregion|terrestrial]] whitlockite from its phase in [[extraterrestrial]] 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 rock]]s. 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, et al., 1996, Klein & Dutrow, 2007). 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. (C. Calvo, and R. Gopal, 1975). 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 [[geology|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 (Jolliff et al. 2006). In the biologic literature, whitlockite and apatite are use interchangeably. Whitlockite is also associated so frequently with apatite in its [[biology|biologic]] occurrences that it is frequent presumed to be apatite. (R.Lagie, et al., 2003). ==Geologic occurrences== Whitlockite has two [[inorganic]] occurrences with geologic significance. The first, known as terrestrial whitlockite, is found as a secondary mineral in granite pegmatites in such areas as Custer Country, South Dakota, as dine crystals associated with quartz at the Tip Top mine, and at the Palermo mine in North Groton, NH (Roberts et al. 1974). The second occurrence is extraterrestrial whitlockite, which is now known as [[merrillite]]. Extraterrestrial whitlockite has been identified in lunar samples as well as [[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 (Jolliff, et al., 2006). ==Biologic occurrences== Whitlockite can also be found in biological systems and has been implicated in several human diseases (Lee, et al., 2006, Lagier and Baud, 2003). Whitlockite can be found at many different sites in the human body, but is particularly concentrated in calcified tissues, such as [[embryonic]] and adult bone. The highest concentrations of whitlockite appear in the [[weight bearing]] area of the [[femoral head]]. (Lagier and Baud, 2003) Traces of whitlockite have also been found in [[tuberculosis|tuberculous]] lesions, [[urinary calculi]] and even [[prostatic]] deposits. Whitlockite can also be found in the oral cavity, where it is a primary component of dental calculi and salivary stones. Lastly, whitlockite can be found in [[aortic]] media, where it may be involved in arteriosclerosis. The presence of whitlockite at these different locations has not attracted much attention from [[biomedical]] scientists or clinicians, chiefly because whitlockite is not visible with the stains used to routinely examine [[microscopic]] sections of healthy or diseased tissue. However, the presence of whitlockite does become obvious when X-ray [[diffraction]] is used to examine these same sections (Lagier and Baud, 2003). In part, whitlockite occurs commonly in biologic systems because of the high concentrations of [[proteolipid]]s and [[divalent]] [[cation]]s 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. (Lagier and Baud, 2003) ==Physical properties== Each of the different phases of whitlockite discussed above exhibit approximately the same physical properties. They display no [[cleavage (crystal)|cleavage]], fracture subconchoidal to uneven, and tend to be brittle. They are classified with a hardness of 5 and a density of 3.12 g/cm3. Color varieties are colorless, white, gray, yellowish or pinkish, and can be transparent to translucent. Whitlockites exhibit a vitreous to resinous [[lustre (mineralogy)|luster]]. The typical habit of whitlockite is [[rhombohedral]] crystals, but whitlockite can also rarely be tabular. The crystal habit of whitlockite also ranges from coarse granular to earthy. ==See also== *[[List of minerals]] *[[List of minerals named after people]] ==References== {{Reflist}} * [http://webmineral.com/data/whitlockite.shtml Webmineral data] Calvo, C., and R. Gopal. (1975) The Crystal Structure of Whitlockite from the Palermo Quarry. American Mineralogist, 60: 120-133. Deer, W.A., R.A. Howie and J. Zussman. (1992) An Introduction to the Rock Forming Minerals, 2nd Edition. Prentice Hall, Harlow 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. 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. Klein C. and B. Dutrow (2008) Mineral Science, 23rd Edition. Wiley, Inc., New York. Lagier R., and C.-A. Baud. (2003). Magnesium whitlockite, a calcium phosphate crystal of special interest in pathology. Pathol. Res. Pract. 199, 329-335. Lee, R.S., M.V. Kayser . S.Y. Ali (2006) Calcium phosphate microcrystal deposition in the human intervertebral disc. J. Anat. 208, 13-9. [[Category:Calcium minerals]] [[Category:Magnesium minerals]] [[Category:Phosphate minerals]] [[it:Whitlockite]]