rhyolite Geol.
(ˈraɪəlaɪt)
Also -lyte.
[ad. G. rhyolith (Jahrb. d. K. K. Geol. Reichs-Anstalt (Wien) (1860) XI. 156), irreg. f. Gr. ῥύαξ stream (of lava) + λίθος stone: see -lite.]
Richthofen's name for a variety of trachyte found in Hungary, containing quartz; later, a general name for volcanic rocks exhibiting a fluidal texture. In mod. use, a type of acidic extrusive volcanic rock, usu. pale in colour and porphyritic in texture, having phenocrysts esp. of quartz or potassium-feldspar in a fine-grained or glassy groundmass which commonly shows flow structure.
| 1868 Mem. Calif. Acad. Sci. I. 50 The name ‘rhyolite’ was proposed, early in 1860, for certain rocks frequently occurring on the southern slope of the Carpathians. 1872 Watts Dict. Chem. 1st Suppl. 1882 Geikie Geol. Sk. 257 Volcanic rocks, chiefly trachytes, rhyolites, obsidians. 1887 Dana Min. 476 Rhyolyte or Quartz-trachyte. 1932 A. Johannsen Descriptive Petrogr. Igneous Rocks II. 268 Most rhyolites are light in colour: white, yellow, brown, or pink, but yellowish green and even deep red rocks are found. 1971 I. G. Gass et al. Understanding Earth i. 22/1 The rock types granite, diorite and gabbro are all coarse-grained and usually found in intrusions. They are matched compositionally by fine-grained rocks, respectively rhyolite, andesite and basalt, which are characteristically found as surface lava flows (extrusions). |
| attrib. 1887 Cassell's Encycl. Dict., Rhyolite-breccia, a breccia consisting almost entirely of fragments of rhyolites. 1897 Geikie Anc. Volcanoes Gt. Brit. I. 19 A rhyolite felsite or allied variety. 1944 A. Holmes Princ. Physical Geol. xx. 455 During the late Pleistocene there were paroxysmal eruptions of rhyolite-tuffs, followed later by flows of rhyolite. 1955 Sci. News Let. 9 July 20/2 The ancient implements are made chiefly of slate and shale but some are of jasper, quartz and rhyolite porphyry (rock of lava origin). 1977 A. Hallam Planet Earth 164/1 Rhyolite eruptions are characteristic of areas of active mountain-building such as island arcs (e.g., Sumatra, Japan, West Indies), and mountain chains such as the Andes. |
Hence
rhyoˈlitic a., pertaining to, resembling, or related to rhyolite.
| 1866 Lawrence tr. Cotta's Rocks Classified 216 The rhyolitic division of the trachytes. 1884 T. G. Bonney in Nature XXX. 193/1 A Rhyolitic Rock from Lake Tanganyika. |