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Llanite is a hypabyssally intruded rhyolite with phenocrysts of microcline and euhedral quartz. The quartz crystals are blue hexagonal bipyramids. The unusual blue coloration of the quartz is thought to be due to ilmenite inclusions.〔Zolensky, M.E., Sylvester, P.J., and Paces, J.B. (1988) ''Origin and significance of blue coloration in quartz from Llano rhyolite (llanite), north-central Llano County, Texas.'' Am. Min. v. 73, p. 313-323.〕 It is named after Llano County, Texas, the only place where it is found (according to locals; however, geologists have identified other locations where this rock may be found, according to Robert Reed.〔Reed, R. nd, (''Llanite in Africa.'' )(''Llanite,'' ) (''Rob's Granite Page'' ), The University of Texas at Austin, Austin, Texas.〕 A dike of llanite crops out on Texas State Highway 16 about 9 miles north of the town of Llano.〔Roadside Geology of Texas, 1991, by Darwin Spearing〕 Llanite is very strong, with a crushing strength of 37,800 lb/in2 or 26,577,180 kg/m2.〔Barnes, Virgil E. (1988) Geological Society of America Centennial Field Guide-- South-Central Section, p. 361-368.〕 Modal mineralogy of llanite mode:〔Iddings, J. P. (1904) Quartz-feldspar-porphyry (graphiphyroliparosealaskose) from Llano, Texas. Journal of Geology, 12, p. 225-231.〕 *quartz - 34.6% *microcline - 27.8% *plagioclase - 27.9% *biotite - 8.6% *fluorite - 1.1% *apatite - 0.14% *magnetite - trace *ilmenite - trace *zircon - trace A large piece of polished llanite can be seen at the Badu House, a historic bed and breakfast in Llano, Texas. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「llanite」の詳細全文を読む スポンサード リンク
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