Whitlockite is a mineral, an unusual form of
calcium phosphate
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 ...
. Its formula is Ca
9(Mg
Fe)(PO
4)
6PO
3O
H.
[ It is a relatively rare mineral but is found in ]granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quart ...
pegmatite
A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...
s, phosphate rock
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxi ...
deposits, guano
Guano (Spanish from qu, wanu) is the accumulated excrement of seabirds or bats. As a manure, guano is a highly effective fertilizer due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. G ...
caves and in chondrite
A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primi ...
meteorite
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
s.[ 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
New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
.[
With regards to ]periodontal
Periodontology or periodontics (from Ancient Greek , – 'around'; and , – 'tooth', genitive , ) is the specialty of dentistry that studies supporting structures of teeth, as well as diseases and conditions that affect them. The supporting ...
dentistry
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the teeth, gums, and mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, disorders, and conditions o ...
, magnesium whitlockite comprises one component of many of the inorganic content of calculus
Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizations of arithm ...
. 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
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
group of minerals with three distinct occurrences. For many years, these occurrences were thought to be identical. However, recent studies using x-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
and electron diffraction
Electron diffraction refers to the bending of electron beams around atomic structures. This behaviour, typical for waves, is applicable to electrons due to the wave–particle duality stating that electrons behave as both particles and waves. Si ...
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
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
. 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
Terrestrial refers to things related to land or the planet Earth.
Terrestrial may also refer to:
* Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...
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
In medicine, a prosthesis (plural: prostheses; from grc, πρόσθεσις, prósthesis, addition, application, attachment), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through trau ...
.
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
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
, which is frequently found as an accessory mineral in many types of rock, including igneous
Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...
and metamorphic rock
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
s. Apatite has also been found in hydrothermal
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
veins and cavities or even Alpine-type veins associated with quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
. The most important varieties of apatite are represented by fluorapatite
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, bl ...
, hydroxyapatite
Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...
, chlorapatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common end ...
and carbonate-apatite
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. A decade later, the Apollo landing missions returned an impressive array of lunar
Lunar most commonly means "of or relating to the Moon".
Lunar may also refer to:
Arts and entertainment
* ''Lunar'' (series), a series of video games
* "Lunar" (song), by David Guetta
* "Lunar", a song by Priestess from the 2009 album ''Prior t ...
rocks as well as other kinds of meteoric material. This unique resource led to an unprecedented barrage of geologic
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...
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. 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.
Bobdownsite is a variety of whitlockite from Yukon, Canada
Yukon (; ; formerly called Yukon Territory and also referred to as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the second-least populated province or territory in Canada, with a population of 43,964 as ...
, that was thought to contain fluorine
Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reacti ...
bonded directly to phosphorus, giving it the chemical formula Ca9(Mg)(PO4)6(PO3F)[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.] 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.
Geological occurrences
Whitlockite has two inorganic
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
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
Custer County is a county in the U.S. state of South Dakota. As of the 2020 United States Census, the population was 8,318. Its county seat is Custer. The county was created in 1875, and was organized in 1877.
Geography
Custer County lies on t ...
, as dine crystals associated with quartz at the Tip Top mine, and at the Palermo mine in North Groton, New Hampshire. The second occurrence is extraterrestrial whitlockite, which is now known as merrillite
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.
Mineral species, sub-group and group
Merrillite is a distinct '' mineral species'' ...
. Extraterrestrial whitlockite has been identified in lunar samples as well as martian
Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. It became the most popular celestial object in fiction in the late 1800s as the Moon was evidently lifeless. At the time, the pred ...
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
Petrogenesis, also known as petrogeny, is a branch of petrology dealing with the origin and formation of rocks. While the word petrogenesis is most commonly used to refer to the processes that form igneous rocks, it can also include metamorphic an ...
of extraterrestrial rocks.
Biological occurrences
Whitlockite can also be found in biological systems and has been implicated in several human diseases. Whitlockite can be found at many sites in the human body, but is particularly concentrated in calcified tissues, such as embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
nic and adult bone. The highest concentrations of whitlockite appear in the weight bearing In orthopedics, weight-bearing is the amount of weight a patient puts on an injured body part. Generally, it refers to a leg, ankle or foot that has been fractured or upon which surgery has been performed, but the term can also be used to refer to r ...
area of the femoral head
The femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur). It is supported by the femoral neck.
Structure
The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...
. Traces of whitlockite have also been found in tuberculous lesions, urinary calculi
Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...
and even prostatic
On either side of the urethral crest is a slightly depressed fossa, the prostatic sinus, the floor of which is perforated by numerous apertures, the orifices of the prostatic ducts from the lateral lobes of the prostate
The prostate is bo ...
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
The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes ox ...
media, where it may be involved in arteriosclerosis. The presence of whitlockite at these places has not attracted much attention from biomedical
Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine) scientists or clinicians, chiefly because whitlockite is not visible with the stains used to routinely examine microscopic
The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...
sections of healthy or diseased tissue. However, the presence of whitlockite becomes obvious when X-ray diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...
is used to examine these sections. In part, whitlockite occurs commonly in biologic systems because of the high concentrations of proteolipid
A proteolipid is a protein covalently linked to lipid molecules, which can be fatty acids, isoprenoids or sterols. The process of such a linkage is known as protein lipidation, and falls into the wider category of acylation and post-translationa ...
s and divalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules.
Description
The combining capacity, or affinity of an ...
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
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.
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
In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a three-dimensional figure with six faces which are rhombus, rhombi. It is a special case of a parallelepiped where all edges are the same length. It c ...
crystals, but whitlockite can also rarely be tabular. The crystal habit of whitlockite also ranges from coarse granular to earthy.[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]
See also
*List of minerals
This is a list of minerals for which there are articles on Wikipedia.
Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various ''species''. Within a m ...
*List of minerals named after people
This is a list of minerals named after people. The chemical composition follows name.
A
*Abelsonite: C31H32N4Ni – American physicist Philip Hauge Abelson (1913–2004)alfred
*Abswurmbachite: Cu2+Mn3+6O8SiO4 – German mineralogist I ...
References
{{Phosphate minerals
Calcium minerals
Magnesium minerals
Phosphate minerals
Trigonal minerals
Minerals in space group 161
Minerals described in 1941