Llanite
Image: James St. John (CC BY 2.0)
Mineral NameLlanite
Chemical FormulaNot applicable (rock), primarily SiO2, Al2O3, K2O, Na2O
Mohs Hardness7
Streak ColorWhite
CleavageNot applicable (rock), constituent feldspar exhibits good cleavage
FractureConchoidal (quartz phenocrysts) to uneven
Specific Gravity2.4
Colorsblue, orange, gray, brown, pink
TransparencyTransparent to translucent (phenocrysts), opaque (groundmass)
Type LocalityLlano Uplift, Texas, USA
Mineral GroupIgneous rock (felsic volcanic/hypabyssal)
Usesbuilding material, aggregate, collector's item
Associated Mineralsquartz, perthitic feldspar, biotite mica
Rarityuncommon
Description
A porphyritic igneous rock characterized by prominent dark bluish quartz and light grayish-orangish perthitic feldspar phenocrysts set within a fine-grained brown groundmass of quartz, feldspar, and biotite mica.
Geological Context
Llanite is a Mesoproterozoic (1.106 Ga) hypabyssal porphyritic rhyolite, indicating formation from shallow intrusive or extrusive volcanic processes in the Llano Uplift region of Texas.
