Overall, 527 carbonatite localities are known on Earth, and they are found on all continents and also on oceanic islands. Most of the carbonatites are shallow intrusive bodies of calcite-rich igneous rocks in form of volcanic necks, dykes, and cone-sheets. These generally occur in association with larger intrusions of alkali-rich silicate igneous rocks. The extrusive carbonatites are particularly rare, only 49 are known, and they appear to be restricted to a few continental rift zones, such as the Rhine valley and the East African rift system. Associated igneous rocks typically include ijolite, melteigite, teschenite, lamprophyres, phonolite, foyaite, shonkinite, silica undersaturated foid-bearing pyroxenite (essexite), and nepheline syenite. Carbonatites are typically associated with undersaturated (low silica) igneous rocks that are either alkali (Na2O and K2O), ferric iron (Fe2O3) and zirconium-rich agpaitic rocks or alkali-poor, FeO-CaO-MgO-rich and zirconium-poor miaskitic rocks. The Mount Weld carbonatite is unassociated with a belt or suite of alkaline igneous rocks, although calc-alkaline magmas are known in the region. The genesis of this Archaean carbonatite remains contentious as it is the sole example of an Archaean carbonatite in Australia. Intrusive morphology Carbonatite is known to form in association with concentrically zoned complexes of alkaline-igneous rocks, the typical example of this being Phalaborwa, South Africa. Carbonatites in the form of sills, lopoliths and rare dikes are reported in the Guyana Shield. The Mud Tank and Mount Weld carbonatites take the form of multi-stage cylindrical intrusive bodies with several distinct phases of carbonatite intrusion. Smaller carbonatite sills and dikes are present in other Proterozoic mobile belts in Australia, typically as dikes and discontinuous pods. Known examples Dozens of carbonatites are known including: the Bearpaw Mountains, Montana the Oka and Saint-Honoré, Quebec; Gem Park and Iron Hill, Colorado; Magnet Cove igneous complex, Arkansas; Mountain Pass, California; the Palabora Complex near Phalaborwa, South Africa; Jacupiranga, Brazil; Ayopaya, Bolivia; Cerro Impacto, Venezuela Kovdor and Vischnevogorsk, Russia, Amba Dongar and Newania from India; Maz, Argentina the Mud Tank and Mount Weld, Australia; the Fen Complex, Norway; part of the basal complex of Fuerteventura, Spain; the Avon Volcanic District, Missouri. In 2017, the discovery of a new carbonatite deposit was confirmed north-west of Prince George, British Columbia, in a region termed the "Rocky Mountain Rare Metal Belt". The volcano Ol Doinyo Lengai, in the East African Rift is the world's only active carbonatite volcano. Other older carbonatite volcanoes are located in the same region, including Mount