Whitlockite
Encyclopedia
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 pegmatite
s, phosphate rock deposits, guano
caves and in chondrite
meteorite
s. 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 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.
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 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
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
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. 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.
, 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. 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.
nic and adult bone. The highest concentrations of whitlockite appear in the weight bearing
area of the femoral head. 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 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. 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.
, 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.
Tricalcium phosphate
Tricalcium phosphate is a calcium salt of phosphoric acid with the chemical formula Ca32. It is also known as tribasic calcium phosphate or "bone ash" ....
. Its formula is Ca9(MgFe
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
)(PO4)6PO3OH
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. It is a relatively rare mineral but is found in granitic pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
s, phosphate rock deposits, guano
Guano
Guano is the excrement of seabirds, cave dwelling bats, and seals. Guano manure is an effective fertilizer due to its high levels of phosphorus and nitrogen and also its lack of odor. It was an important source of nitrates for gunpowder...
caves and in chondrite
Chondrite
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids...
meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s. 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
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
, NY, USA.
With regards to periodontal dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...
, 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 phosphatePhosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
group of minerals with three distinct occurrences. For many years, these occurrences were thought to be identical. However, recent studies using x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
and electron diffraction
Electron diffraction
Electron diffraction refers to the wave nature of electrons. However, from a technical or practical point of view, it may be regarded as a technique used to study matter by firing electrons at a sample and observing the resulting interference pattern...
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
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. 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
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
, which is frequently found as an accessory mineral in many types of rock, including igneous and metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
s. Apatite has also been found in hydrothermal veins and cavities or even Alpine-type veins associated with quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
. The most important varieties of apatite are represented by fluorapatite
Fluorapatite
Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral with the formula Ca53F . Fluorapatite is a hard crystalline solid. Although samples can have various color , the pure mineral is colorless as expected for a material lacking transition metals...
, hydroxyapatite, chlorapatite 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
Groton, New Hampshire
Groton is a town in Grafton County, New Hampshire, United States. The population was 593 at the 2010 census.- History :The town was originally named Cockermouth in honor of Charles Wyndham, Baron Cockermouth and Earl of Egremont, who was Secretary of State for the Southern Department from 1761 to...
. 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
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
rocks as well as other kinds of meteoric material. This unique resource led to an unprecedented barrage of geologic
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
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
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
occurrences that it is frequent presumed to be apatite.
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 DakotaCuster County, South Dakota
As of the census of 2000, there were 7,275 people, 2,970 households, and 2,067 families residing in the county. The population density was 5 people per square mile . There were 3,624 housing units at an average density of 2 per square mile...
, 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. Extraterrestrial whitlockite has been identified in lunar samples as well as martian
Martian
As an adjective, the term martian is used to describe anything pertaining to the planet Mars.However, a Martian is more usually a hypothetical or fictional native inhabitant of the planet Mars. Historically, life on Mars has often been hypothesized, although there is currently no solid evidence of...
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
Petrogenesis, also known as petrogeny, is a branch of petrology dealing with the origin of igneous rocks. Petrology is the branch of geology dealing with the origin, occurrence, structure and history of igneous, metamorphic, and sedimentary rocks....
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 different sites in the human body, but is particularly concentrated in calcified tissues, such as embryoEmbryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic and adult bone. The highest concentrations of whitlockite appear in the weight bearing
Weight bearing
In orthopedics, weight-bearing is the amount of weight a patient puts on the leg on which surgery has been performed. In general, it is described as a percentage of the body weight, because each leg of a healthy person carries the full body weight when walking, in an alternating fashion.After...
area of the femoral head. Traces of whitlockite have also been found in tuberculous
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
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
Microscopic
The microscopic scale is the scale of size or length used to describe objects smaller than those that can easily be seen by the naked eye and which require a lens or microscope to see them clearly.-History:...
sections of healthy or diseased tissue. However, the presence of whitlockite does become obvious when X-ray diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
is used to examine these same sections. In part, whitlockite occurs commonly in biologic systems because of the high concentrations of proteolipids and divalent
Divalent
In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent....
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.
Physical properties
Each of the different phases of whitlockite discussed above exhibit approximately the same physical properties. They display no cleavageCleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
, 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
Lustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....
. 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.