What is Greenstone belt?
[[File:Archean Greenstone Pillow Lava in Michigan USA 3.jpg|thumb|250px|Greenstone from Michigan]] '''Greenstone belts''' are large regions of very ancient [[Metamorphic rock|metamorphosed]] [[volcanic]] rocks. The name comes from the green colour of the [[mineral]]s in the rocks. [[Chlorite]], [[actinolite]] and other green [[amphibole]]s are the typical green minerals. Greenstone belts were originally formed of [[igneous]] rocks, such as [[basalt]]. The belts formed at ancient oceanic spreading centers and in volcanic island arcs. They may be several thousand kilometres long. Later, they were metamophosed, with minor [[sedimentary rock]]s in-between the volcanic formations. Those greenstone belts which formed in ancient oceans are now found on land in [[Archaean]] and [[Proterozoic]] [[craton]]s between [[granite]] and [[gneiss]] bodies. The rocks are [[mafic]], meaning they are high in [[magnesium]] and [[silica]]. [[Category:Metamorphic rocks]]