sedimentary

Chert (specifically Agate/Jasper variety)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5-7 on Mohs scale. Color: Waxy brown, honey-yellow, and tan. Luster: Waxy to vitreous. Crystal structure: Hexagonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.

Hardness: 6
Color: Waxy brown, honey-yellow, and tan
Luster: Waxy to vitreous

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich fluids in cavities within volcanic or sedimentary rocks. This specimen likely originated as a secondary mineral deposit in a host rock during the Cenozoic or Mesozoic eras and was later weathered out and water-worn.

Uses & applications

Used widely for lapidary work (jewelry, cabochons), tumbled stones for collecting, and historically used for stone tools due to its sharp conchoidal fracture.

Geological facts

This specimen shows the transition between common chert and semi-translucent agate. Geologists often look for 'conchoidal' (shell-like) fractures—visible on the edges of this piece—as a primary way to identify silica-rich rocks.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy texture, and the way it breaks into smooth, curved surfaces rather than flat planes. Common in riverbeds and gravel pits.

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