Llanite
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 [1]. It is named after Llano County, Texas, the only place where it is found (according to locals, however geologists have identified other locations this rock may be found according to Dr. Robert Reed , a geology professor at The University of Texas at Austin). A dike of llanite outcrops on Texas State Highway 16 about 9 miles north of the town of Llano[2].
Llanite is very strong with a crushing strength of 37,800 lb. per sq. inch or 26,577,180 kg per sq. m [3].
Llanite Mode [4]
- quartz - 34.6%
- microcline - 27.8%
- plagioclase - 27.9%
- biotite - 8.6%
- fluorite - 1.0%
- apatite - 0.13%
- magnetite - trace
- ilmenite - trace
- zircon - trace
The largest piece of polished Llanite in the world can be found at the Badu House, a historic bed and breakfast in Llano, Texas.
[edit] References
- ^ 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.
- ^ Roadside Geology of Texas, 1991, by Darwin Spearing
- ^ Barnes, Virgil E. (1988) Geological Society of America Centennial Field Guide-- South-Central Section, p. 361-368.
- ^ Iddings, J. P. (1904) Quartz-feldspar-porphyry (graphiphyroliparosealaskose) from Llano, Texas. Journal of Geology, 12, p. 225-231.
 |
This article related to petrology is a stub. You can help Wikipedia by expanding it. |
