Talk:Magnetite/@comment-26507296-20150702072033/@comment-25145798-20150702073111

Magnetite forms in small quantities interspersed with many iron-rich minerals, but only forms bodies of crystals on its own when mafic magma, a very liquid magma laden with heavy elements, cools sufficiently slowly for individual crystals to clump together. Magnetite can also form during metamorphism of impure iron-rich limestone. (Source )