Note 3 — Chapter XXII · IRON, COBALT, AND NICKEL

The hydrated ferric oxide is found in nature in a dual form. It is somewhat rarely met with in the form of a crystalline mineral called göthite, whose specific gravity is 4·4 and composition Fe2H3O4, or FeHO2—that is, one of oxide of iron to one of water, Fe2O3,H2O; frequently found as brown ironstone, forming a dense mass of fibrous, reniform deposits containing 2Fe2O3,3H2O—that is, having a composition Fe4H6O9. In bog ore and other similar ores we most often find a mixture of this hydrated ferric oxide with clay and other impurities. The specific gravity of such formations is rarely as high as 4·0.