Whitlockite

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Whitlockite
Whitlockite-RoyalOntarioMuseum-Jan18-09.jpg
An example of the mineral Whitlockite on display at the Royal Ontario Museum.
General
Category Phosphate minerals
Formula
(repeating unit)		Ca9(Mg,Fe++)(PO4)6(PO3OH)
IMA symbol Wht [1]
Strunz classification 8.AC.45
Crystal system Trigonal
Crystal class Ditrigonal pyramidal (3m)
H-M symbol: (3m)
Space group R3c
Unit cell a = 10.33, c = 37.103(5) [Å]; Z = 3
Identification
ColorColorless, gray-white, light pink, light yellow
Crystal habit rhombohedral crystals, often tabular, massive, microcrystalline crusts and as "cave pearls"
Cleavage None
Fracture Brittle
Tenacity Brittle
Mohs scale hardness5
Luster Vitreous to resinous
Streak White
Diaphaneity Transparent
Density 3.13
Optical propertiesUniaxial (−)
Refractive index nω = 1.629 nε = 1.626
Birefringence δ = 0.003
Other characteristics Piezoelectric and pyroelectric
References [2] [3] [4]

Whitlockite is a mineral, an unusual form of calcium phosphate. Its formula is Ca9(MgFe)(PO4)6PO3OH. [2] [3] [4] It is a relatively rare mineral but is found in granitic pegmatites, 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]

Contents

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 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 [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 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 [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 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 County, South Dakota, as dine crystals associated with quartz at the Tip Top mine, and at the Palermo mine in North Groton, New Hampshire. [12] 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. [13]

Biological occurrences

Whitlockite can also be found in biological systems and has been implicated in several human diseases. [5] [14] Whitlockite can be found at many 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. [5] Traces of whitlockite have also been found in 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 places 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 becomes obvious when X-ray diffraction is used to examine these sections. [5] In part, whitlockite occurs commonly in biologic systems because of the high concentrations of proteolipids and divalent 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 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 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. [15]

See also

Related Research Articles

<span class="mw-page-title-main">Amblygonite</span>

Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite forms a series with montebrasite, the low fluorine endmember. Geologic occurrence is in granite pegmatites, high-temperature tin veins, and greisens. Amblygonite occurs with spodumene, apatite, lepidolite, tourmaline, and other lithium-bearing minerals in pegmatite veins. It contains about 10% lithium, and has been utilized as a source of lithium. The chief commercial sources have historically been the deposits of California and France.

<span class="mw-page-title-main">Pegmatite</span> Igneous rock with very large interlocked crystals

A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than 1 cm (0.4 in) and sometimes greater than 1 meter (3 ft). Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic composition to granite. However, rarer intermediate composition and mafic pegmatites are known.

<span class="mw-page-title-main">Apatite</span> Mineral group, calcium phosphate

Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ion, respectively, in the crystal. The formula of the admixture of the three most common endmembers is written as Ca10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6F2 and Ca10(PO4)6Cl2.

<span class="mw-page-title-main">KREEP</span> Geochemical component of some lunar rocks, potassium, lanthanides, and phosphorus

KREEP, an acronym built from the letters K, REE and P, is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat enhanced concentration of a majority of so-called "incompatible" elements and the heat-producing elements, namely radioactive uranium, thorium, and potassium.

<span class="mw-page-title-main">Anorthosite</span> Mafic intrusive igneous rock composed predominantly of plagioclase

Anorthosite is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.

<span class="mw-page-title-main">Calcium phosphate</span> Chemical compound

The term calcium phosphate refers to a family of materials and minerals containing calcium ions (Ca2+) together with inorganic phosphate anions. Some so-called calcium phosphates contain oxide and hydroxide as well. Calcium phosphates are white solids of nutritional value and are found in many living organisms, e.g., bone mineral and tooth enamel. In milk, it exists in a colloidal form in micelles bound to casein protein with magnesium, zinc, and citrate–collectively referred to as colloidal calcium phosphate (CCP). Various calcium phosphate minerals are used in the production of phosphoric acid and fertilizers. Overuse of certain forms of calcium phosphate can lead to nutrient-containing surface runoff and subsequent adverse effects upon receiving waters such as algal blooms and eutrophication (over-enrichment with nutrients and minerals).

<span class="mw-page-title-main">Autunite</span>

Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–2+1⁄2. Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals, commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.

<span class="mw-page-title-main">Brazilianite</span>

Brazilianite, whose name derives from its country of origin, Brazil, is a typically yellow-green phosphate mineral, most commonly found in phosphate-rich pegmatites.

<span class="mw-page-title-main">Enstatite</span> Pyroxene: magnesium-iron silicate with MgSiO3 and FeSiO3 end-members

Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) – ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO
3, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En80Fs20).

<span class="mw-page-title-main">Wavellite</span> Aluminium phosphate basic hydrate mineral

Wavellite is an aluminium basic phosphate mineral with formula Al3(PO4)2(OH, F)3·5H2O. Distinct crystals are rare, and it normally occurs as translucent green radial or spherical clusters.

<span class="mw-page-title-main">Tricalcium phosphate</span> Chemical compound

Tricalcium phosphate (sometimes abbreviated TCP), more commonly known as Calcium phosphate, is a calcium salt of phosphoric acid with the chemical formula Ca3(PO4)2. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid of low solubility. Most commercial samples of "tricalcium phosphate" are in fact hydroxyapatite.

<span class="mw-page-title-main">Fluorapatite</span> Phosphate mineral

Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, yellow, violet, or colorless), the pure mineral is colorless, as expected for a material lacking transition metals. Along with hydroxylapatite, it can be a component of tooth enamel, but for industrial use both minerals are mined in the form of phosphate rock, whose usual mineral composition is primarily fluorapatite but often with significant amounts of the other.

Xanthoxenite is a rare calcium iron(III) phosphate mineral with formula: Ca4Fe3+2(PO4)4(OH)2·3H2O. It occurs as earthy pale to brownish yellow incrustations and lath shaped crystals. It crystallizes in the triclinic crystal system. It occurs as an alteration product of triphylite in pegmatites. It occurs associated with apatite, whitlockite, childrenite–eosphorite, laueite, strunzite, stewartite, mitridatite, amblygonite and siderite.

<span class="mw-page-title-main">Anapaite</span> Hydrous phosphate mineral

Anapaite is a calcium–iron phosphate mineral with formula: Ca2Fe2+(PO4)2·4H2O. It is a mineral that typically occurs in cavities in fossil bearing sedimentary rocks. It is also found in phosphate bearing iron ores and rarely in pegmatites. It is commonly found with goethite, siderite and vivianite.

<span class="mw-page-title-main">Springwater meteorite</span> Meteorite found in Canada

The Springwater meteorite is a stony-iron pallasite, found near Springwater, Saskatchewan in 1931. At that time the find consisted of three large masses (38.6 kilograms, 18.6 kilograms and 10.6 kilograms. Other fragments have been found recently, including a 53 kilograms individual in 2009 that is now in the Royal Ontario Museum.

<span class="mw-page-title-main">Ludlamite</span>

Ludlamite is a rare phosphate mineral with chemical formula (Fe,Mn,Mg)3(PO4)2·4H2O. It was first described in 1877 for an occurrence in Wheal Jane mine in Cornwall, England and named for English mineralogist Henry Ludlam (1824–1880).

Bobfergusonite is a mineral with formula Na2Mn5FeAl(PO4)6. The mineral varies in color from green-brown to red-brown. It was discovered in 1986 in Manitoba, Canada, and named for Robert Bury Ferguson (born 1920). As of 2012, the mineral has only been found in Canada and Argentina.

Merrillite is a calcium phosphate mineral with the chemical formula Ca9NaMg(PO4)7. It is an anhydrous, sodium-rich member of the merrillite group of minerals.

<span class="mw-page-title-main">Grayite</span>

Grayite, ThPO4·(H2O), is a thorium phosphate mineral of the Rabdophane group first discovered in 1957 by S.H.U. Bowie in Rhodesia. It is of moderate hardness occurring occasionally in aggregates of hexagonal crystals occasionally but more commonly in microgranular/cryptocrystalline masses. Due to its thorium content, grayite displays some radioactivity although it is only moderate and the mineral displays powder XRD peaks without any metamict-like effects. The color of grayite is most commonly observed as a light to dark reddish brown but has also been observed as lighter yellows with grayish tints. It has a low to moderate hardness with a Mohs hardness of 3–4 and has a specific gravity of 3.7–4.3. It has been found in both intrusive igneous and sedimentary environments.

<span class="mw-page-title-main">Serrabrancaite</span>

Serrabrancaite is a mineral with the chemical formula MnPO4•H2O and which is named for the locality where it was found, the Alto Serra Branca Pegmatite. The Alto Serra Branca mine has been in operation since the 1940s. It is located in Paraiba, Brazil near a village named Pedra Lavrada. Tantalite is the main mineral mined here. Specimens of serrabrancaite are kept in the Mineralogical Collections of both the Bergakademie Freiberg, Germany and the Martin-Luther Universität Halle, Institut für Geologische Wissenschaften.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 Whitlockite: Whitlockite mineral data from Mindat
  3. 1 2 3 Whitlockite Mineral Data from Webmineral
  4. 1 2 3 http://rruff.geo.arizona.edu/doclib/hom/whitlockite.pdf Handbook of Mineralogy
  5. 1 2 3 4 5 6 Lagier, R.; Baud, C.-A. (2003). "Magnesium Whitlockite, a Calcium Phosphate Crystal of Special Interest in Pathology". Pathology - Research and Practice. 199 (5): 329–335. doi:10.1078/0344-0338-00425. 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. ↑ McCubbin, Francis M.; Phillips, Brian L.; Adcock, Christopher T.; Tait, Kimberly T.; Steele, Andrew; Vaughn, John S.; Fries, Marc D.; Atudorei, Viorel; Vander Kaaden, Kathleen E.; Hausrath, Elisabeth M. (1 August 2018). "Discreditation of bobdownsite and the establishment of criteria for the identification of minerals with essential monofluorophosphate (PO3F2–)". American Mineralogist. 103 (8): 1319–1328. doi:10.2138/am-2018-6440. 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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