Frederick William Rudler

“ MAGNETITE, a mineral forming the natural magnet (see Magnetism) , and important also as an iron-ore. It is an iron-black, opaque mineral, with metallic lustre; hardness about 6, sp. gr. 4.9 to 5.2. When scratched, it yields a black streak. It is an oxide of iron having the formula Fe3O4, corresponding with 72.4% of metal, whence its great value as an ore. It may be regarded as a ferroso-ferric oxide, FeO.Fe2O3, or as iron ferrate, Fe′′Fe2′′′O4. Titanium is often present, and occasionally the mineral contains magnesium, nickel, &c. It is always strongly magnetic. ”

“ In some cases it appears to have segregated from a basic eruptive magma, and in other cases to have resulted from metamorphic action. Certain deposits appear to have been formed, directly or indirectly, by wet processes. ”