Under all these three conditions the diamond is associated with fragments of the rocks of the country and the minerals derived from them, 'especially quartz, hornstone, jasper, the polymorphous oxide of titanium (rutile, anatase and brookite), oxides and hydrates of iron (magnetite, ilmenite, haematite, limonite), oxide of tin, iron pyrites, tourmaline, garnet, xenotime, monazite, kyanite, diaspore, sphene, topaz, and several phosphates, and also gold.
Bog iron ore is an impure limonite, usually formed by the influence of micro-organisms, and containing silica, phosphoric acid and organic matter, sometimes with manganese.
On exposure to meteoric influences pyrites commonly becomes brown, by formation of ferric hydrate or limonite, whence the change is called "limonitization."
They are four important iron ores, magnetite, haematite, limonite and siderite, and one of less but still considerable importance, pyrite or pyrites.
Limonite, 2Fe20 3, 3H 2 0, contains 59.9% of iron.