Seifertite
Encyclopedia
Seifertite is a silicate mineral
with the formula SiO2 and is one of the densest polymorphs of quartz
. It has only been found in Martian and lunar meteorite
s where it is presumably formed from either tridymite
or cristobalite
– other polymorphs of quartz
– as a result of heating during the atmospheric re-entry and impact to the Earth, at an estimated minimum pressure of 35 GPa. It can also be produced in the laboratory by compressing cristobalite in a diamond anvil cell
to pressures above 40 GPa. The mineral is named after Friedrich Seifert
(1941- ), the founder of the Bayerisches Geoinstitut at University of Bayreuth
, Germany, and is officially recognized by the International Mineralogical Association
.
Seifertite forms micrometre-sized crystalline lamellae embedded into a glassy SiO2 matrix. The lamellae are rather difficult to analyze as they vitrify within seconds under laser or electron beams used for standard Raman spectroscopy
or electron beam microanalysis
, respectively, even at much reduced beam intensities. Nevertheless, it was possible to verify that it is mainly composed of SiO2 with minor inclusions of Na2O
(0.40 wt.%) and Al2O3
(1.14 wt.%). X-ray diffraction reveals that the mineral has scrutinyite
(α-PbO2) type structure with an orthorhombic symmetry and Pbcn or Pb2n space group
. Its lattice constants a = 4.097, b = 5.0462, c = 4.4946, Z = 4 correspond to the density of 4.294 g/cm3 which is among the highest among any forms of silica (cf. density of quartz is 2.65 g/cm3). Only stishovite
has a comparable density of about 4.3 g/cm3.
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
with the formula SiO2 and is one of the densest polymorphs of 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,...
. It has only been found in Martian and lunar meteorite
Lunar meteorite
A Lunar meteorite is a meteorite that is known to have originated on the Moon.-Discovery:In January 1982, John Schutt, leading an expedition in Antarctica for the ANSMET program, found a meteorite that he recognized to be unusual...
s where it is presumably formed from either tridymite
Tridymite
Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. Its chemical formula is SiO2. Tridymite was first described in 1868 and the type location is in Hidalgo,...
or cristobalite
Cristobalite
The mineral cristobalite is a high-temperature polymorph of silica, meaning that it has the same chemical formula, SiO2, but a distinct crystal structure. Both quartz and cristobalite are polymorphs with all the members of the quartz group which also include coesite, tridymite and stishovite...
– other polymorphs of 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,...
– as a result of heating during the atmospheric re-entry and impact to the Earth, at an estimated minimum pressure of 35 GPa. It can also be produced in the laboratory by compressing cristobalite in a diamond anvil cell
Diamond anvil cell
A diamond anvil cell is a device used in scientific experiments. It allows compressing a small piece of material to extreme pressures, which can exceed 3,000,000 atmospheres ....
to pressures above 40 GPa. The mineral is named after Friedrich Seifert
Friedrich Seifert
Friedrich Alfred Seifert is a German mineralogist and geophysicist. He is the founding director of Bayerisches Geoinstitut at University of Bayreuth. A silicate mineral seifertite is named after him.-Life and work:...
(1941- ), the founder of the Bayerisches Geoinstitut at University of Bayreuth
University of Bayreuth
The University of Bayreuth is a public research university situated in Bayreuth, Germany. It was founded in 1975 as a campus university focusing on international collaboration and interdisciplinarity...
, Germany, and is officially recognized by the International Mineralogical Association
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...
.
Seifertite forms micrometre-sized crystalline lamellae embedded into a glassy SiO2 matrix. The lamellae are rather difficult to analyze as they vitrify within seconds under laser or electron beams used for standard Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
or electron beam microanalysis
X-ray fluorescence
X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material that has been excited by bombarding with high-energy X-rays or gamma rays...
, respectively, even at much reduced beam intensities. Nevertheless, it was possible to verify that it is mainly composed of SiO2 with minor inclusions of Na2O
Sodium oxide
Sodium oxide is a chemical compound with the formula Na2O. It is used in ceramics and glasses, though not in a raw form. Treatment with water affords sodium hydroxide....
(0.40 wt.%) and Al2O3
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
(1.14 wt.%). X-ray diffraction reveals that the mineral has scrutinyite
Scrutinyite
Scrutinyite is a rare oxide mineral and is the alpha crystalline form of lead dioxide , plattnerite being the other, beta form. The mineral was first reported in 1988 and its name reflects the scrutiny and efforts required to identify it from a very limited amount of available sample...
(α-PbO2) type structure with an orthorhombic symmetry and Pbcn or Pb2n space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
. Its lattice constants a = 4.097, b = 5.0462, c = 4.4946, Z = 4 correspond to the density of 4.294 g/cm3 which is among the highest among any forms of silica (cf. density of quartz is 2.65 g/cm3). Only stishovite
Stishovite
Stishovite is an extremely hard, dense tetragonal form of silicon dioxide. It was long considered the hardest known oxide; however, boron suboxide has recently been discovered to be much harder...
has a comparable density of about 4.3 g/cm3.