sedimentary

Quartz Geode Pebble

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Brownish exterior with clear to white crystalline interior; Luster: Vitreous (glassy) inside, dull/earthy outside; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture).

Hardness: 7 (Mohs scale)
Color: Brownish exterior with clear to white crystalline interior
Luster: Vitreous (glassy) inside, dull/earthy outside

Identified July 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as a secondary mineral precipitate in hollow cavities (vugs) within sedimentary or volcanic rocks. Over geological time, silica-rich groundwater fills these cavities and slowly crystallizes. This specific specimen appears to be a river-worn or tumbled version of such a geode fragment.

Uses & applications

Primarily collected as a decorative specimen, used in homeschooling/educational kits, and occasionally used in lapidary work for jewelry if the quality is high.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. These small 'geode' nodules are often referred to as 'potato stones' before they are broken open to reveal their crystalline centers.

Field identification & locations

Look for rounded pebbles that feel unusually light for their size (indicating a hollow center) or show crystalline windows like this one. Commonly found in riverbeds, gravel pits, and desert washes.