gabbron.
/ˈɡabrəʊ/, U.S. /ˈɡæˌbroʊ/ Geology.
A dark, coarse-grained igneous rock formed from the crystallization of basic magma and consisting mainly of plagioclase feldspar (typically labradorite or bytownite), pyroxene (typically augite), iron oxides (typically magnetite), and often olivine.
ΚΠ
1776 R. E. Raspe tr. J. J. Ferber Trav. Italy xix. 274 The hills about Impruneta consist of Gabbro [Ger. Gabbro] or Serpentine-stone.
1837 J. D. Dana Syst. Mineral. 288 Saussurite occurs in primitive regions, and with hornblende and augite constitutes the rocks called gabbro and euphotide.
1874 Q. Jrnl. Geol. Soc. 30 253 The great masses of gabbro in Rum often exhibit that pseudo-stratification so often observed in igneous rocks.
1923 Geogr. Jrnl. 62 197 An even closer resemblance..is provided by the aspect of the Coolin in Skye, where, however, the rock is black gabbro.
1969 G. M. Bennison & A. E. Wright Geol. Hist. Brit. Isles iii. 68 The Malvernian is composed predominantly of metamorphosed igneous rocks, diorites and gabbros.
2007 Trail Feb. 46/1 I found myself falling down it [sc. a gully], pursued by two tons of unfettered gabbro.
Derivatives
gaˈbbroic adj. of or relating to gabbro; of the nature of or resembling gabbro.
ΚΠ
1884 Science July 71/1 Eruptions of gabbroic and granitic rocks must be admitted as important elements in its [sc. the Cascade Range's] construction.
1930 Times 8 Feb. 11/4 Plutonic igneous rocks, both granitic and gabbroic, there are met, less abundantly.
1990 C. Pellant Rocks, Minerals & Fossils 23/1 Norite has a medium- to coarse-grained texture and gabbroic composition.
2010 New Scientist 20 Nov. 18/1 You would travel through sediment, a layer of basalt, and then hit the gabbroic layer, which lies directly above the mantle.
gabbroˈitic adj. now rare = gabbroic adj.
ΚΠ
1889 17th Ann. Rep. Geol. & Nat. Hist. Surv. Minnesota 1888 96 It would naturally be supposed that this ore is gabbroitic magnetite and therefore titaniferous.
1895 Jrnl. Geol. (Chicago) 3 1 The rarity of olivine in the granulitic rocks is in marked contrast with its abundance in the gabbroitic variety.
2016 Ore Geol. Rev. 72 247/2 The host tuff is underlain by a thick rhyolitic volcanite, crosscut by several gabbroitic dykes in the vicinity of the deposits.
This entry has been updated (OED Third Edition, June 2018; most recently modified version published online March 2022).
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n.1776