Also found in: Encyclopedia, Wikipedia.


Containing magnesium and iron and only a very small amount of silica. Used of igneous rock.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Geological Science) (of such igneous rocks as peridotite) containing less than 45 per cent silica
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˌʌl trəˈbeɪ sɪk)

(of rocks) containing iron and magnesium, with little or no silica.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
Dissolved oxygen (7.8 [+ or -] 3.7 mg L-1) and temperature (28.2 [+ or -] 5.9[degrees]C) was recorded with an oximeter (YSI[MR] model 55), and pH (7.8 [+ or -] 0.6) was recorded with a pH meter (Denver instrument[R] ultraBASIC).
It occurs in basic and ultrabasic igneous rocks and in the metamorphic and sedimentary rocks that are produced when chromite-bearing rocks are altered by heat or weathering.
[USPRwire, Tue Oct 09 2018] Pyroxenite is an ultrabasic rock that consists of minerals that belong to the pyroxenes group-- predominantly, ferromagnesian minerals other than olivine.
Throughout the complex there are sills of gabbro, ultrabasic rocks and dacite porphyrite.
Maroon marble (Elazig cherry) is made of carbonated ultrabasic rocks, serpentinite (Figure 1) and red-green pebbles are attached with the same-coloured cement.
There is no direct evidence exactly to show the formation time of C[O.sub.2] fluids were affected by F19 faults, but the isotopic age chlorite thermal alteration and the fission track age of the calcite veins of ultrabasic have proved that C[O.sub.2] hydrothermal activity was concentrated in this period [12].
Quite common in basic and ultrabasic rocks, Co is a rare metal existing in porphyritic igneous rocks in small quantities (Dixon, 2012).
Invertebrates in the litter and soil at a range of altitudes on Gunung Silam, a small ultrabasic mountain in Sabah.
Relatively high levels of K (about 7%) and low concentrations of Ca (about 2%) in all samples along the Bengal coast can be attributed to the weathering of basic and ultrabasic igneous rock in the drainage area of the rivers.