Ferrous metasilicate, FeSiO₃

Ferrous metasilicate, FeSiO₃, has been prepared by fusing the calculated quantities of ferric oxide and silica at 1600° C. Density, 3.44. It melts at 1500°-1550° C.

The heat of formation of ferrous metasilicate is: -

[FeCO₃] + [SiO₂] = [FeSiO₃] + (CO₂) -7600 calories.
[FeO] + [SiO₂] = [FeSiO₃] + 5000 calories (5905 calories).

Double metasilicates of magnesium and iron occur as the minerals hypersthene and anthophyllite (Mg, Fe)SiO₃. A sodium ferrous metasilicate, NaFe(SiO₃)₂, occurs as dark brown or green prisms in quartz under the name of acmite or cegirite, and a crystalline substance of similar composition has been prepared by Weyberg by fusing silicic acid, ferric hydroxide, and sodium carbonate with excess of sodium chloride. The potassium analogue KFe(SiO₃)₂ has been prepared, but does not apparently occur in nature.

Crystals of ferrous manganese metasilicate (Fe, Mn)SiO₃, or iron rhodonite, have been obtained from Bessemer slags. They belong to the triclinic system, and closely resemble crystals of the mineral.