sedimentary

Jasper or Chert with Quartz Vugs

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and grey with white quartz patches; Luster: Dull to waxy, vitreous in quartz areas; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, tan, and grey with white quartz patches
Luster: Dull to waxy, vitreous in quartz areas

Identified April 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater filling cavities (vugs) in limestone or volcanic ash. The brown color comes from iron oxide impurities. These can range from millions to hundreds of millions of years old depending on the host formation.

Uses & applications

Commonly used for lapidary work (cabs or tumbling), decorative garden stones, and as a collector specimen. Historically used for making tools like scrapers or arrowheads due to its hardness and sharp edges.

Geological facts

This specimen appears to be 'vuggy,' meaning it has small cavities filled with secondary minerals, likely quartz or calcite. Silica-rich rocks like this are extremely resistant to weathering, which is why they are often found as loose stones in riverbeds.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its waxy texture. It is often found in areas with sedimentary limestone or ancient volcanic activity. Collectors should look for the 'sparkle' of small crystals in the recessed areas.