Wikipedia
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. 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. A dike of llanite crops out on Texas State Highway 16 about 9 miles north of the town of Llano.
Llanite is very strong, with a crushing strength of 37,800 lb/in or 26,577,180 kg/m.
Modal mineralogy of llanite mode:
- 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.