igneous

Banded Rhyolite (or Gray Shale pebble)

Rhyolite (SiO2 with minor impurities)

Hardness: 6-7 (Mohs scale), Color: light gray to blue-gray, Luster: dull to earthy, Crystal structure: aphanitic to porphyritic, Cleavage: none, Specific gravity: 2.4-2.6

Identified May 29, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6-7 (Mohs scale), Color: light gray to blue-gray, Luster: dull to earthy, Crystal structure: aphanitic to porphyritic, Cleavage: none, Specific gravity: 2.4-2.6

Formation & geological history

Formed through the rapid cooling of silica-rich lava at or near the Earth's surface during volcanic eruptions. Most surface specimens are from the Cenozoic era.

Uses & applications

Used primarily as crushed stone for road construction, landscaping, and occasionally as decorative gravel or for tumbling by amateur collectors.

Geological facts

Rhyolite is the extrusive equivalent of granite; its rapid cooling prevents large crystal growth, resulting in its fine-grained texture.

Field identification & locations

Identify by its light color, fine-grained texture, and hardness (it will usually scratch glass). Commonly found in volcanic mountain ranges and volcanic island arcs.

Other igneous specimens

See all

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral