Llanite
Llanite is a hypabyssally intruded variety of 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. 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/in2 or 26,577,180 kg/m2.
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
