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Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals.
Llanite comes from a hypabyssal porphyritic rhyolite dike that intrudes Precambrian metamorphics in the 
However, the geology of North-East Africa is very similar to that of Texas. Many of the minerals and fossils found are only found in these two locations on the whole planet.
(geologists have identified other locations where similar types of rock may be found).Reed, R. nd
''Llanite in Africa.''''Rob's Granite Page''
, The University of Texas at Austin, Austin, Texas.
''Llanite and the Blue Quartz of Texas.''
The Backbender's Gazette. vol. XLV, no. 5, pp. 5–12.
Houston Gem and Mineral Society, Houston, Texas
. Igneous rocks {{petrology-stub
Llano Uplift
The Llano Uplift is a geologically ancient, low geologic dome that is about in diameter and located mostly in Llano, Mason, San Saba, Gillespie, and Blanco counties, Texas. It consists of an island-like exposure of Precambrian igneous and m ...
of central Texas. Published radiometric dating on this llanite indicates that it's 1.106 billion years old (late Mesoproterozoic).
The quartz crystals found in llanite are blue hexagonal bipyramids. The unusual blue coloration of the quartz is thought to be due to ilmenite
Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...
inclusions.
It is named after Llano County, Texas
Llano County is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 census, its population was 21,243. Its county seat is Llano, and the county is named for the Llano River.
During the American Civil War, the c ...
, the only place where it is found.
However, the geology of North-East Africa is very similar to that of Texas. Many of the minerals and fossils found are only found in these two locations on the whole planet.
(geologists have identified other locations where similar types of rock may be found).Reed, R. nd''Llanite in Africa.''
, The University of Texas at Austin, Austin, Texas.
dike
Dyke (UK) or dike (US) may refer to:
General uses
* Dyke (slang), a slang word meaning "lesbian"
* Dike (geology), a subvertical sheet-like intrusion of magma or sediment
* Dike (mythology), ''Dikē'', the Greek goddess of moral justice
* Dikes ...
of llanite crops out on Texas State Highway 16
State Highway 16 (SH 16) is a south–north state highway in the U.S. state of Texas that runs from Zapata on the boundary with Mexico to U.S. Highway 281 south of Wichita Falls. It is the longest state highway in Texas at almost , but is o ...
approximately nine miles north of the town of Llano.
Llanite, which is similar to granite, is very strong, with a crushing strength of 37,800 lb/in2 or 26,577,180 kg/m2. Llanite is also very similar in appearance to pietersite.
Modal mineralogy of llanite:Iddings, J. P. (1904) Quartz-feldspar-porphyry (graphiphyro liparose-alaskose) 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
See also
* PorphyryReferences
External links
Heinrich, P. V., 2014''Llanite and the Blue Quartz of Texas.''
The Backbender's Gazette. vol. XLV, no. 5, pp. 5–12.
Houston Gem and Mineral Society, Houston, Texas
. Igneous rocks {{petrology-stub