igneous
Llanite (Rhyolite with Blue Quartz)
Porphyritic Rhyolite
Hardness: 6.5-7 (Mohs). Color: Brownish-red to dark gray matrix with phenocrysts of blue quartz and salmon-colored feldspar. Luster: Vitreous to waxy on phenocrysts, dull on matrix. Crystal structure: Porphyritic.
- Hardness
- 6
- Luster
- Vitreous to waxy on phenocrysts, dull on matrix
Identified More igneous →
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Brownish-red to dark gray matrix with phenocrysts of blue quartz and salmon-colored feldspar. Luster: Vitreous to waxy on phenocrysts, dull on matrix. Crystal structure: Porphyritic.
Formation & geological history
Llanite is a hypabyssal igneous rock that formed as a dike during the Precambrian period, approximately 1.1 billion years ago, when magma cooled quickly near the surface but allowed larger crystals to grow beforehand.
Uses & applications
Primarily used as a decorative stone, in lapidary work for cabochons and jewelry, and as a highly sought-after specimen for geological collectors.
Geological facts
Llanite is famous for its unique blue quartz crystals, which owe their color to ilmenite inclusions. It is named after Llano County, Texas, where the most famous outcropping occurs.
Field identification & locations
Identify by looking for the distinctive 'glowing' blue hexagonal quartz crystals embedded in a dark rhombohedral matrix. It is found almost exclusively in the Llano Uplift of central Texas.
