| Seifertite | |
|---|---|
 Crystal structure | |
| General | |
| Category | Tectosilicates,quartzgroup |
| Formula | SiO2 |
| IMA symbol | Sft[1] |
| Strunz classification | 4.DA.05 (oxides) |
| Dana classification | 75.01.06 (tectosilicates) |
| Crystal system | Orthorhombic (Pbcn) |
| Crystal class | Dipyramidal (mmm) H–M symbol: (2/m 2/m 2/m) |
| Identification | |
| Formula mass | 60.08 g/mol |
| Crystal habit | Microscopic crystals |
| Specific gravity | 4.294 |
| References | [2][3] |
Seifertite is asilicate mineral with the formula SiO2 and is one of the densest polymorphs ofsilica. It has only been found inMartian[4][5] andlunar meteorites,[6] where it is presumably formed from eithertridymite orcristobalite – other polymorphs ofquartz – as a result of heating during theatmospheric entry and impact to the Earth, at an estimated minimal pressure of 35 GPa. It can also be produced in the laboratory by compressing cristobalite in adiamond anvil cell to pressures above 40 GPa. The mineral is named afterFriedrich Seifert (born 1941), the founder of the Bayerisches Geoinstitut atUniversity of Bayreuth, Germany, and is officially recognized by theInternational Mineralogical Association.[4][5][7]
Seifertite forms micrometre-sized crystallinelamellae 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 standardRaman spectroscopy orelectron-beam microanalysis, even at much reduced beam intensities. Nevertheless, it was possible to verify that it is mainly composed of SiO2 with minor inclusions ofNa2O (0.40 wt.%) andAl2O3 (1.14 wt.%).X-ray diffraction reveals that the mineral hasscrutinyite (α-PbO2) type structure with anorthorhombic symmetry and Pbcn or Pb2nspace group. Its lattice constantsa = 4.097,b = 5.0462,c = 4.4946,Z = 4 correspond to the density of 4.294 g/cm3, which is among the highest for any forms of silica (for example, the density of quartz is 2.65 g/cm3).[3][4][5] Onlystishovite has a comparable density of about 4.287 g/cm3.[8]
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| Cryptocrystalline | |||||||||
| Amorphous | |||||||||
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