Alforsite
Encyclopedia
Alforsite is a barium phosphate chloride
mineral with formula: Ba5(PO4)3Cl. It was discovered in 1981, and named to honor geologist
John T. Alfors (1930–2005) of the California Geological Survey
for his work in the area where it was discovered.
Alforsite is a hexagonal
colorless crystal
in the chemical class phosphate
s and the group apatite
. It is found in certain parts of central California
, primarily Fresno
, Mariposa
, and Tulare
Counties. It has also been found in Baja California
, Mexico
.
Alforsite is a constituent of the apatite
group of minerals. It crystallizes in the hexagonal crystal system
with a point group of 6/m and space group P63/m. It occurs as colorless grains that are hard to distinguish from fluoroapatite, as they both display low birefringence and high relief.
, and fluorapatite
were used as standards for the elements they contain. The chemical analysis revealed that traces of Mn, S, Si, and Pb were present and provided computational formulas of (Ba4.68Sr0.19Ca0.13)(P2.98Si0.01)O11.96(Cl0.99F0.05) and (Ba4.05Ca0.75Sr0.24Pb0.03)(P2.94Si0.01)O11.93(Cl0.93F0.14).
atom in the unit cell is enclosed by nine oxygen
atoms with a mean distance of 2.824 Å. Another barium atom is surrounded by six oxygen atoms with a mean distance of 2.791 Å and 3.230 Å, which creates two crystallographically distinctive barium atoms. The phosphate
group in alforsite forms a regular tetrahedron.
intrusions in Fresno
and Mariposa
counties, California. John T. Alfors’ colleagues named the mineral in his honor for his works with rare barium minerals of the sanbornite deposits.
Alforsite was first discovered in samples from the Big Creek locality. Electron microprobe analysis of a thin-section of the sample from Big Creek revealed the new mineral, which resembled ordinary apatite. Rare barium
minerals, mainly silicates, can be uncovered in sanbornite deposits of eastern Fresno and Mariposa counties, California. Alforsite is found in metamorphic sanbornite quartz
, which occurs within a few hundred meters of granodiorite
intrusions, and foliated
quartzite
. Gneissic banded rocks contain the mineral, which has been shown to be associated with witherite
, sanbornite
, and celsian
in samples (with quartz-rich and gillespite-rich bands) from Incline. In order for the witherite- sanbornite-quartz to be stable, temperatures of 500 °C to 600 °C and pressures of 1-3 kbar are required.
exhibit the structural typology of apatite
. This can pose problems and confusion because alforsite bears an almost exact resemblance to other barium
silicates, which exemplifies its group Greek name, apatao, meaning, “I am misleading”. The only way to differentiate alforsite from other barium minerals is through microchemical analysis (Walstrom and Leising, 2005). This misleading mineral emulates the physical and structural features of apatite and is analogously similar to chlorapatite, providing alfrosite with the alternate name, barium chlorapatite. Alforsite has a low birefringence and a high relief resembling fluorapatite in thin-section.. A reddish-violet cathodoluminescence appears on thin-section showing major levels of chlorine
, phosphorous, and barium
.
Alforsite can be recognized by electron microprobe analysis or by intense violet fluorescence in the 10-15 kV electron beam of a luminoscope
.
Halide mineral
The halide mineral class include those minerals with a dominant halide anion . Complex halide minerals may also have polyatomic anions in addition to or that include halides.Examples include the following:*Halite NaCl*Sylvite KCl...
mineral with formula: Ba5(PO4)3Cl. It was discovered in 1981, and named to honor geologist
Geologist
A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...
John T. Alfors (1930–2005) of the California Geological Survey
California Geological Survey
Although it was not until 1880 that the California State Mining Bureau, predecessor to the California Geological Survey, was established, the "roots" of California's state geological survey date to an earlier time...
for his work in the area where it was discovered.
Alforsite is a hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
colorless crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
in the chemical class phosphate
Phosphate
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...
s and the group 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...
. It is found in certain parts of central California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, primarily Fresno
Fresno County, California
Fresno County is a county located in the Central Valley of the U.S. state of California, south of Stockton and north of Bakersfield. As of the 2010 census, it is the tenth most populous county in California with a population of 930,450, and the sixth largest in size with an area of . The county...
, Mariposa
Mariposa County, California
Mariposa County is a county in the U.S. state of California, located in the western foothills of the Sierra Nevada mountains. It lies north of Fresno, east of Merced, and southeast of Stockton. As of the 2010 census, the population was 18,251 up from 17,130 at the 2000 census...
, and Tulare
Tulare County, California
Tulare County is a county located in the Central Valley of the U.S. state of California, south of Fresno. Sequoia National Park is located in the county, as are part of Kings Canyon National Park, in its northeast corner , and part of Mount Whitney, on its eastern border...
Counties. It has also been found in Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
.
Alforsite is a constituent of the 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...
group of minerals. It crystallizes in the hexagonal crystal system
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
with a point group of 6/m and space group P63/m. It occurs as colorless grains that are hard to distinguish from fluoroapatite, as they both display low birefringence and high relief.
Composition
Alforsite’s ideal chemical formula is Ba5(PO3)4Cl. Chemical analysis of the composition of alfrosite was demonstrated by the use of an Ortex current digitizer and an electron microbe. Synthetic barium chlorapatite, strontianiteStrontianite
Strontianite is an important raw material for the extraction of strontium. It is a rare carbonate mineral and one of only a few strontium minerals...
, and 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...
were used as standards for the elements they contain. The chemical analysis revealed that traces of Mn, S, Si, and Pb were present and provided computational formulas of (Ba4.68Sr0.19Ca0.13)(P2.98Si0.01)O11.96(Cl0.99F0.05) and (Ba4.05Ca0.75Sr0.24Pb0.03)(P2.94Si0.01)O11.93(Cl0.93F0.14).
Structure
Alforsite exhibits Lau symmetry 6/m. It is concluded that the space group is P63/m because every single apatite compound possess that space group. The parameters of the unit cell are a=10.25 Å and c=7.64 Å. One bariumBarium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
atom in the unit cell is enclosed by nine oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
atoms with a mean distance of 2.824 Å. Another barium atom is surrounded by six oxygen atoms with a mean distance of 2.791 Å and 3.230 Å, which creates two crystallographically distinctive barium atoms. The phosphate
Phosphate
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 in alforsite forms a regular tetrahedron.
Geologic occurrence
It is found crystallizing in the massive metasedemintary rock, sanbornite, which is found near granodioriteGranodiorite
Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...
intrusions in Fresno
Fresno
Fresno is the fifth largest city in California.Fresno may also refer to:-Places:Colombia* Fresno, TolimaSpain* Fresno, a ghost village in Nidáliga, Valle de Sedano, Burgos* Aldea del Fresno, Madrid* Fresno de la Vega, Ribera del Esla, León...
and Mariposa
Mariposa
Mariposa is the Spanish word for "butterfly". In Portuguese, it is both a synonym for "moth" and "butterfly" .It may also refer to:-Canada:* Mariposa, Saskatchewan, a rural municipality...
counties, California. John T. Alfors’ colleagues named the mineral in his honor for his works with rare barium minerals of the sanbornite deposits.
Alforsite was first discovered in samples from the Big Creek locality. Electron microprobe analysis of a thin-section of the sample from Big Creek revealed the new mineral, which resembled ordinary apatite. Rare barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
minerals, mainly silicates, can be uncovered in sanbornite deposits of eastern Fresno and Mariposa counties, California. Alforsite is found in metamorphic sanbornite 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,...
, which occurs within a few hundred meters of granodiorite
Granodiorite
Granodiorite is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. It usually contains abundant...
intrusions, and foliated
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...
quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
. Gneissic banded rocks contain the mineral, which has been shown to be associated with witherite
Witherite
Witherite is a barium carbonate mineral, BaCO3, in the aragonite group. Witherite crystallizes in the orthorhombic system and virtually always is twinned. The mineral is colorless, milky white, grey, pale yellow, green, to pale brown. The specific gravity is 4.3, which is high for a translucent...
, sanbornite
Sanbornite
Sanbornite is a rare barium phyllosilicate mineral with formula BaSi2O5. Sanbornite is a colorless to white to pale green, platey orthorhombic mineral with Mohs hardness of 5 and a specific gravity of 3.74....
, and celsian
Celsian
Celsian is an uncommon feldspar mineral, barium aluminosilicate, BaAl2Si2O8. The mineral occurs in contact metamorphic rocks with significant barium content. Its crystal system is monoclinic, and it is white, yellow, or transparent in appearance. In pure form, it is transparent...
in samples (with quartz-rich and gillespite-rich bands) from Incline. In order for the witherite- sanbornite-quartz to be stable, temperatures of 500 °C to 600 °C and pressures of 1-3 kbar are required.
Special characteristics
Synthetic alforsite has environmental importance because it may be used to replicate contamination by lead without the harmful affects of lead toxicity. For this reason, remediation of metal in soil can be practiced. Synthetic alforsite is prepared in a laboratory and mixed with soil to create a polluted soil, and then is treated with a mixture of salt and ammonium dihydrogen phosphate and maintained at a pH level of nine for two weeks.Physical properties
Alforsite occurs as colorless, miniscule subhedral grains with a diameter less than 0.05 :mm. However, on rare occasions, it can crystallize to a diameter up to 0.2 :mm. Minerals that belong to different groups, such as silicates, and sulfatesSulfate mineral
The sulfate minerals are a class of minerals which include the sulfate ion within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal veins and as secondary minerals in the oxidizing zone of sulfide mineral deposits...
exhibit the structural typology of 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...
. This can pose problems and confusion because alforsite bears an almost exact resemblance to other barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
silicates, which exemplifies its group Greek name, apatao, meaning, “I am misleading”. The only way to differentiate alforsite from other barium minerals is through microchemical analysis (Walstrom and Leising, 2005). This misleading mineral emulates the physical and structural features of apatite and is analogously similar to chlorapatite, providing alfrosite with the alternate name, barium chlorapatite. Alforsite has a low birefringence and a high relief resembling fluorapatite in thin-section.. A reddish-violet cathodoluminescence appears on thin-section showing major levels of chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, phosphorous, and barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
.
Alforsite can be recognized by electron microprobe analysis or by intense violet fluorescence in the 10-15 kV electron beam of a luminoscope
Origin of the name
The mineral Alforsite was named for John T. Alfors in recognition of his extensive research of the type locality of barium minerals and other related rare and new minerals. John T. Alfors was a highly regarded geologist and mineralogist who worked for the state Division of Mines and Geology in CaliforniaCalifornia
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.