Ilmenite. Titanium iron oxide, m FeTiO3 + n Fe2O3.
Iron Pyrites. Iron disulphide, FeS2. A cubic species, Pyrite, and a less common rhombic species, Marcasite, occur.
Kaolin. Hydrous aluminium silicate, H4Al2Si2O9.
Kyanite. Aluminium silicate, Al2SiO5, crystallised in the triclinic system. See [Andalusite].
Labradorite. See [Felspars].
Leucite. Potassium aluminium silicate, KAl(SiO3)2.
Limonite. Hydrous iron oxide. H6Fe4O9.
Magnetite. Magnetic iron oxide, Fe3O4.
Marcasite. See [Iron Pyrites].
Micas. A series of aluminium silicates, with potassium, magnesium, or iron, or all of these. Lithium and sodium sometimes occur. The two marked types are Muscovite, rich in aluminium and potassium, the common "alkali mica," H2KAl3(SiO4)3, with a silvery aspect, and Biotite, the common dark "ferromagnesian" mica, (H, K)2(Mg, Fe″)2(Al, Fe‴)2(SiO4)3.