pegmatoidadj.n.
/ˈpɛɡmətɔɪd/, U.S. /ˈpɛɡməˌtɔɪd/ Geology.
A. adj.
Resembling or similar in structure to pegmatite, but usually lacking a graphic appearance; consisting of a rock of this nature.
ΘΚΠ
the world > the earth > structure of the earth > constituent materials > rock > igneous rock > [adjective] > plutonic > granite > varieties of
pegmatitic1878
pegmatoid1889
1889 Amer. Naturalist 23 261 Messrs. Diller and Whitfield have identified the blue mineral present in fibres penetrating the quartz and plagioclase of the pegmatoid portion of a biotite gneiss at Harlem, N. Y., as demortierite [read dumortierite].
1920 A. Holmes Nomencl. Petrol. 178 Pegmatoid, a term suggested to denote very coarse-grained facies of igneous rock having a pegmatite-habit, but differing from pegmatite proper by the absence of graphic texture.
1964 Amer. Mineralogist 49 434 Cutting across the banding at slight angles are pegmatoid veinlets.
1999 I. Kostov & R. I. Kostov Crystal Habits Minerals vi. 203 In pegmatoid and quartz veins, kyanite crystals are, as a rule, long-prismatic.
B. n.
A pegmatoid rock.
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1934 Webster's New Internat. Dict. Eng. Lang. (ed. 2) Pegmatoid, a pegmatite containing a feldspathoid as an essential constituent... [Also] a coarse-grained pegmatite of normal habit, disting[uished] from graphic granite.
1972 Philos. Trans. (Royal Soc.) A. 271 522 Scheelite and wolframite mineralization within the Piriwiri system..occurs as dissemination pegmatoids and quartz veins.
2003 Mining Jrnl. (Nexis) 1 Aug. 79 The estimate, based on the UG2 chromitite layer, includes a 25% discount for geological losses such as faults, potholes, dykes and pegmatoids.
This entry has been updated (OED Third Edition, September 2005; most recently modified version published online March 2022).
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adj.n.1889