ultrabasicadj.n.
/ʌltrəˈbeɪsɪk/ Geology.
Of an igneous rock: having a silica content that is lower than that of the basic rocks (cf. basic adj. 2b), spec. less than 45 per cent by weight. Also as n.
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the world > the earth > structure of the earth > constituent materials > rock > igneous rock > [adjective] > mineral composition
basic1854
acid1859
ultrabasic1881
femic1902
sal1909
ultramafic1933
komatiitic1975
the world > the earth > structure of the earth > constituent materials > rock > igneous rock > [noun] > mineral composition
fem1902
sal1902
ultramafic1933
ultrabasic1964
komatiite1969
1881 J. W. Judd Volcanoes (ed. 2) 317 There are some rarer materials..that present a most wonderful resemblance to the stony portions of meteorites. These materials we may call ‘ultra-basic rocks’.
1885 J. W. Judd in Q. Jrnl. Geol. Soc. 41 354 Those rocks which contain an excessive proportion of the bases, especially magnesia and ferrous oxide, and are therefore composed largely of unisilicates, may be conveniently classed as ultra-basic rocks.
1893 A. Geikie Text-bk. Geol. (ed. 3) vi. i. 681 Crystalline rocks, which range from amorphous masses..to basic or even what are called ‘ultra-basic’ compounds.
1898 Nature 3 Feb. 315/2 He..had arrived at certain very definite views concerning the constant association of the crystalline form of carbon with the ultrabasic rocks.
1938 R. W. Lawson tr. G. von Hevesy & F. A. Paneth Man. Radioactivity (ed. 2) xxv. 274 Stone meteorites are still more strongly basic than the ultrabasic terrestrial rocks.
1964 Economic Geol. LIX. 804 In the low-lying regions the ultrabasics are largely masked by soil.
1970 Nature 28 Mar. 1227/2 Most of the volcanics were basic, but during the upper Cretaceous ultrabasics..were intruded.
1977 Sci. Amer. Mar. 96/3 In a typical greenstone belt early volcanic activity has produced ultrabasic and basic lavas.
This entry has not yet been fully updated (first published 1986; most recently modified version published online June 2018).
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adj.n.1881