Ultrabasic Rock

Ultrabasic Rock


a rock composed chiefly of iron-magnesium silicates—olivine and pyroxene—with small admixtures of secondary minerals, such as chromite and magnesite. Chemically, ultrabasic rocks are relatively poor in Si02 (less than 45 percent) and rich in magnesium (more than 42 percent MgO). There are many different types of ultrabasic rocks. The most important types are the dunites, the olivinites (in which magnetite is present instead of chlorite), the peridotites, and the pyroxenites. Characteristic of ultrabasic rocks is the full or partial conversion of olivine and pyroxene into the serpentine minerals, such as chryso-tile, antigorite, and lizardite, with the formation of serpentinites. Ultrabasic rocks are widely distributed as massifs or tectonic detached masses in all regions of development of magmatic rocks and are also found in the region of the midoceanic ridges. They are often associated with gabbros, alkaline rocks, and carbona-tites. Lava flows of ultrabasic rocks were studied in Australia in the early 1970’s. Effusive ultrabasic rocks have been found in Siberia (maimechites) and on Kamchatka.

The conditions of the formation of ultrabasic rocks have not been fully established. Most tectonic geologists, for example, A. V. Peive, A. L. Knipper, and V. G. Kaz’min, believe that ultrabasic rocks are tectonic, detached masses of rock from the upper mantle, whereas many petrographers, in particular, V. N. Lodochnikov and the Americans H. Taylor and P. Wyllie, continue to develop the idea of the magmatic genesis of ultrabasic rocks.

Many types of mineral deposits are associated with ultrabasic rocks: asbestos and nephrite deposits, silicate deposits, and deposits of the ores of platinum, chromium, nickel, and alloyed iron.


Peive, A. V. “Okeanicheskaia kora geologicheskogo proshlogo.” Geotektonika, 1969, no. 4.
Wyllie, P. J. “The Origin of the Ultramafic and Ultrabasic Rocks.” Tectonophysics, 1969, vol. 7, nos. 5-6.


References in periodicals archive ?
Within and adjacent to the Olive Highlands, ultrabasic bedrock (harzburgite) is found only just outside the periphery in the north-east, in upper Wadi Hayl and Wadi Saham, at elevations well below the main ridges, but some ultrabasic rock types can be found within what is mapped as a mixed unit, along the short ridge west of the Jebel Qitab summit ridge (separating uppermost Wadi Hiluw from Wadi Hayl) and continuing north along the lower slopes of the Olive Highlands, east of Jebel Sfai and Jebel Samah (British Geological Survey 2006a, Thomas et al.
The parent material of the very deep red, clayey soil is highly fractured and serpentinised ultrabasic rock (peridotite) of Upper Cretaceous origin.
From here, there is a steep climb over a patch of ultrabasic rock (former oceanic floor pushed up by the granite).
Jebel Rais, in Oman, is an isolated promontory of carbonate sediments within that intervening area of ultrabasic rock (rising to 1800+ metres above uppermost Wadi Hawasina) and for that reason was the subject of a botanical reconnaissance in by the senior author (GRF) in December 2005.
The state of Quindio has geological units of oceanic and continental origin which date back to Paleozoic and Mesozoic ages (Arquia complex, Quebradagrande complex, ultrabasic rock fragments, and Cordoba igneous complex) which are intruded into by igneous units from the late Mesozoic and overlaid by tertiary sedimentary sequences.
Two opportunities exist to increase resources; a careful assessment of platinum occurrence in ultrabasic rock masses (western Tuva, eastern Sayan, Koryakia) and a detailed study of platinum in black shale sequences, particularly in those locations where the association of platinum with gold mineralisation has already been revealed.
The measurement was conducted on a weathered block of ultrabasic rock.
The slow percolation of groundwater through ultrabasic rock in an arid climate also produces exceptionally alkaline groundwater, with pH as high as 11.