flows in the Archaean greenstone belts. Here, the pyroxenite lavas are created by in-situ crystallisation and accumulation of pyroxene at the base of a lava flow, creating the distinctive spinifex texture, but also occasionally mesocumulate and orthocumulate segregations. This is in essence similar to the formation of olivine spinifex textures in komatiite lava flows, the chemistry of the magma differing only to favor crystallisation of pyroxene. A type locality is the Gullewa Greenstone Belt, in the Murchison region of Western Australia, and the Duketon Belt near Laverton, where pyroxene spinifex lavas are closely associated with gold deposits. Distribution They frequently occur in the form of dikes or segregations in gabbro and peridotite: in Shetland, Cortland on the Hudson River, North Carolina (websterite), Baltimore, New Zealand, and in Saxony. They are also found in the Bushveld Igneous Complex in South Africa and The Great Dyke in Zimbabwe. The pyroxenites are often subject serpentinization under low temperature retrograde metamorphism and weathering. The rocks are often completely replaced by serpentines, which sometimes preserve the original structures of the primary minerals, such as the lamination of hypersthene and the rectangular cleavage of augite. Under pressure-metamorphism hornblende is developed and various types of amphibolite and hornblende-schist are produced. Occasionally rocks rich in pyroxene are found as basic facies of nepheline syenite; a good example is provided by the melanite pyroxenites associated with the borolanite variety found in the Loch Borralan igneous complex of Scotland. References Lambart, S. L., and others, 2016, The role of pyroxenite in basalt genesis: Melt-PX, a melting parameterization for mantle pyroxenites between 0.9 and 5 GPa, Journal of Geophysical Research - Solid Earth 121, p. 5708–5735 Sobolev, A. V., and others, 2007, The amount of recycled crust in sources of mantle-derived melts, Science 316, p. 412-417 (abstract) Retrieved on 6 October 2007 External links Ultramafic rocks Plutonic rocks Volcanic rocks