Hypersthene

enstatite

metamorphic

Hypersthene is a term used for a mineral part way between enstatite and ferrosilite. It is not a valid mineral name.
Formulae:
Hypersthene (Mg,Fe)SiO3
Enstatite MgSiO3
Ferrosilite FeSiO3
Properties of hypersthene:
Specific gravity:
Hardness: 5½ to 6
Streak: Greyish white, greenish
Colour: Greyish white
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Metamorphic environments

Hypersthene occurs in igneous rocks and schist and as pyroclasts (particles ejected during a volcanic eruption). It also may be found in basalt.

Alteration

augite and CO2 to hypersthene, calcite and quartz
Ca(Mg,Fe)Si2O6 + CO2 → (Mg,Fe)SiO3 + CaCO3 + SiO2

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4
(DHZ 2A p258)

jadeite, diopside, magnetite and quartz to aegirine, kushiroite (pyroxene) and hypersthene
2NaAlSi2O6 + CaMgSi2O6 + Fe2+Fe3+2O4 + SiO2 ⇌ 2NaFe3+Si2O6 + CaAlAlSiO6 + MgFeSi2O6
Aegirine in blueschist facies rocks may be formed by the above reaction (DHZ 2A 512).

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