igneous

Banded Rhyolite

Rhyolite (felsic volcanic rock)

Hardness: 6-7 (Mohs). Color: Light gray, buff, or tan with dark gray or black bands. Luster: Dull to vitreous. Crystal structure: Aphanitic (fine-grained) with flow banding. Cleavage: None. Specific gravity: 2.4-2.6.

Hardness: 6-7 (Mohs)
Color: Light gray, buff, or tan with dark gray or black bands
Luster: Dull to vitreous

Identified May 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed from viscous, silica-rich volcanic lava that cooled rapidly on or near the Earth's surface. The distinct bands are caused by laminar flow of the lava during eruption and crystallization.

Uses & applications

Used primarily as decorative stone, in lapidary work for making cabochons, and sometimes as crushed stone in construction or road building.

Geological facts

Flow banding in rhyolite is a classic example of liquid movement preserved in stone; the bands represent layers of high and low viscosity that were stretched during the eruption.

Field identification & locations

Identify by crisp, fine-grained parallel or wavy bands and high silica content (scratching glass). Common in volcanic fields such as those in the Western United States (Utah, Nevada).

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mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous