Elgoresyite, first discovered during the crystallographic study of the
Suizhou meteorite, is a naturally occurring, high-pressure iron-magnesium silicate mineral. High-pressure polymorphs of magnesium silicates have been rarely discovered on Earth, due to retrograding as they ascend to the surface. It is named after Ahmed El Goresy.
Occurrence
Currently, Elgoresyite has only been known to occur in the shock-induced melt veins of the Suizhou meteorite. These veins are ~300 μm in thickness. It is found in association with the minerals
ringwoodite
Ringwoodite is a high-pressure phase of Mg2SiO4 (magnesium silicate) formed at high temperatures and pressures of the Earth's mantle between depth. It may also contain iron and hydrogen. It is polymorphous with the olivine phase forsterite (a ...
,
olivine
The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
, tetragonal ringwoodite,
taenite
Taenite is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with a chemical formula of and nickel proportions of 20% up to 65%.
The name is derived from the Greek ταινία for "band, ribbo ...
, and MgSiO
3 rich glass.
Appearance and properties
Physical properties such as color, luster, streak, hardness, tenacity, cleavage, fracture, and density could not be determined due to small grain size of the only known sample available. Optical properties as well were not able to be determined for this same reason. Density (calc) however is 4.315 g/cm
3. This was based on the empirical formula and single-crystal XRD data.
Chemical properties
The empirical formula is (Mg
3.38Si
1.95Fe
2+1.60Al
0.05Na
0.03Ca
0.02)
Σ = 7.03O
9. The simplified and ideal chemical formula is (Mg,Fe,Si)
7O
9.
Crystallography
The crystal system is
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...
, and the
space group
In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that ...
is ''C''2/''m'' (#12). The
unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector
In mathematics, a unit vector i ...
parameters are :a = 9.397(2) Å, b = 2.763(1) Å, c = 11.088(3) Å, β = 94.25(2)°, volume V =287.10(14) Å
3, and number of formulas per unit cell, Z = 2.
References
{{Reflist
Monoclinic minerals
Meteorite minerals