Iron sesqui-oxide

Ferric oxide, Iron sesqui-oxide, Fe203, occurs in abundant quantities in nature, both in the massive and crystalline forms, the former being known as red haematites, whilst the latter are termed specular iron (see p. 16) when the crystals are rhombohedra and scalcnohcdra, or micaceous iron when in thin translucent scales. 

At the same time, clay materials and sand release silica (SiO ), alumina (Al Oj), iron sesqui-oxide (FejO,) and lose their constitutive water (H O). On melting, these oxides produce, according to the following chemical reactions listed below, four new definite stoichiometric synthetic minerals. 

Specular Iron Ore—1led Hematite.—This is a sesqui-oxide of iron existing in great abundance, and found in a variety of shapes, both massive and in crystals. The following are a few of the crystalline forms in which It fa found—Figs. 272,273, 274. The crystals are of... 

Accumulation of clay, iron, aluminum, humus, or in combination residual concentration of sesquioxides or clay or mixed sesqui-oxide coatings giving darker, stronger, redder colors or has granular, blocky, or prismatic structure. 

Ferric selenide or iron sesqui-selenide, Fe2Se3, was obtained by Little 2 by heating iron to redness in selenium vapour, cooling, and fusing the product with excess of selenium under a layer of borax. It also results when hydrogen selenide is passed over ferric oxide at red heat.3 It is a grey crystalline powder. 

The low mobility of phosphorus in the soil is due to the fact that this element occurs mostly in the form of phosphates, which are frequently converted to sparingly soluble or insoluble compounds. In acid soils, these are particularly compounds of phosphorus with iron and aluminium sesqui-oxides. 

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