Elgoresyite

Elgoresyite, first discovered during the crystallographic study of the Suizhou meteorite, is a naturally occurring, high-pressure iron-magnesium silicate mineral. High-pressure poly morphs 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.[3]

Elgoresyite
General
Categorysilicate mineral
Formula
(repeating unit)		(Mg,Fe)5Si2O9
IMA symbolEgo[1]
Strunz classification09.
Crystal systemMonoclinic
Space groupC2/m
Unit cella = 9.397 Å, b = 2.763 Å
c = 11.088 Å;
β=94.25°; Z = 2
Identification
Colorundetermined
Crystal habitsubhedral
Cleavageundetermined
Fractureundetermined
Tenacityundetermined
Mohs scale hardnessundetermined
Lusterundetermined
Streakundetermined
DiaphaneityTransparent
Density4.315 g/cm3
Optical propertiesundetermined
Refractive index(n=Kc*D+1) is 1.95
Melting point~2000K at ~23 GPa
References[2]

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, olivine, tetragonal ringwoodite, taenite, and MgSiO3 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/cm3. This was based on the empirical formula and single-crystal XRD data.

Chemical properties

The empirical formula is (Mg3.38Si1.95Fe2+1.60Al0.05Na0.03Ca0.02)Σ = 7.03O9. The simplified and ideal chemical formula is (Mg,Fe,Si)7O9.

Crystallography

The crystal system is monoclinic, and the space group is C2/m (#12). The unit cell 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) Å3, and number of formulas per unit cell, Z = 2.

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Bindi, L., et al., 2021, Discovery of Elgoresyite, (Mg,Fe)5Si2O9: Implications for Novel Iron-Magnesium Silicates in Rocky Planetary Interiors (accessed November,December 2021).<https://pubs.acs.org/doi/abs/10.1021/acsearthspacechem.1c00157>
  3. "Ahmed el Goresy (1934-2019)".
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