of ultramafic rock units and small occurrences of ultramafic rocks. This map is derived from the Geologic Map of California (1:750,000 scale - one inch equals about 12 miles), Jennings (1977). Instead, alteration of pyroxenes and plagioclases forms other hydrated minerals such as amphibole, chlorite, and talc, which also modify the physical properties of these rocks. It is poor in silica, in the 40% or less range. Tectonized ultramafic complexes in western Sierra Nevada and western Klamath Mts., primarily of Ordovician to Early Jurassic age. 2a-c). In hand specimen, chromite is mostly easily seen in fresh specimens of dunite . Ultramafic rocks contain a high levels of iron and manganese, low levels of silica and high concentration of such toxic elements as nickel, chromium, and cobalt, the soil resembles the oxisols on basic igneous rocks, but they are variable as the forest they bear. ultramafic rocks and serpentinite of the mafic and ultramafic complex of the Catalina amphibolite unit are ... ites and pelitic schists that contain quartz + Ano8 plagioclase + muscovite + garnet + bio- tite, 2 kyanite, zoisite, rutile, magnetite, ilmenite, chlorite, and graphite. This area is mantled by a pelagic sediment cover, overlying exposures of unconsolidated serpentine muds that contain serpentinized clasts of mafic and ultramafic rocks (Fryer et al., 1985, 1990). . Sulfide bodies containing Ni, Cu and PGE are commonly found in pyroxenitic layers near the stratigraphic level that plagioclase first becomes a cumulus mineral (150 m below to 500 m above the mafic-ultramafic boundary) or mineralisation may also occur at the base of cyclic units (Hoatson, 1998). A granite that contains significant amounts of epidote. Ultramafic Rocks ... assuming excess H 2 O. Peridotites also contain an aluminous phase, either plagioclase, spinel, or garnet. These rocks are also known as ultrabasic rocks. In ultramafic rocks, almost all of the iron is associated with various mafic silicates minerals, so there is no iron oxide phase present . The Earth’s mantle consists predominantly of ultramafic rocks. Ultramafic rocks ( ultramafites or ultramafolites) are igneous and metamorphic rocks that consist predominantly of mafic (ferromagnesian) and related minerals.The more important primary mafic minerals are olivine, pyroxene, hornblende, mica, garnet, and opaque ores; the most abundant secondary or metamorphic minerals are serpentine, chlorite, amphibole, epidote, and magnetite. Peridotite is an ultrabasic rock consisting of olivine, with or without pyroxene, whereas picrite, in addition to ferromagnesian minerals, may contain up to 10% feldspar. Mineralogical Changes in Ultramafic Rocks. As a result, a distinctive type of vegetation develops on these soils. The structural relations between the ultramafic rocks and the "country rock" are seen best in the Silla Gibara hill mass 5 km southeast of Gibara. Ultramafic rocks originate in the Earth’s mantle and are pushed up to the surface in mountain building events or they are carried to the Earth’s surface as nodules (xenoliths or inclusions) with basalt magma. Subtopics: Hornblendite Peridotite Pyroxenite. ULTRAMAFIC COMPLEXES Ultramafic complexes can be divided into three major categories: Alpine, Alaskan and Layered intrusive types. Ultramafic definition, ultrabasic. Gabbroids from the Berezovka massif contain ultramafic xenoliths. Mafic rocks are low in silica, in the 45-50% range. More than 700 different types of igneous rocks are known. Earth material; Plutonic rock; Ultramafic intrusive rock. Peridotite contains mainly olivine and pyroxene with small amounts of other minerals such as garnet and spinel. The igneous rock texture helps in identifying the rock origin, mode of crystallization, and classification of the rock. If enough chromite is present, the rock may become an ore of chromium. 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