Sedimentary

Jasper and Agate (Polished Pebble)

Chalcedony (SiO2 with impurities)

Hardness: 6.5-7 on Mohs scale. Color: Multicolored (yellow, white, brown). Luster: Waxy to vitreous. Crystal Structure: Microcrystalline/Cryptocrystalline trigonal. Cleavage: None (Conchoidal fracture). Specific Gravity: 2.6-2.65.

Hardness: 6
Color: Multicolored (yellow, white, brown)
Luster: Waxy to vitreous

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from silica-rich groundwater filling cavities in volcanic or sedimentary rocks. The yellow and brown hues are caused by iron oxides (limonite/goethite). It is likely from the Cenozoic era, though similar specimens form across various geological ages.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), interior decoration, and as a collector's specimen. It is valued for its ability to take a high polish and its unique patterns.

Geological facts

Jasper is technically an opaque variety of chalcedony, while Agate is the translucent variety. This specimen is a mix of both. The name 'Jasper' is derived from the Greek 'iaspis', meaning 'spotted stone'.

Field identification & locations

Identify in the field by its smooth, waxy surface when wet and its inability to be scratched by a steel knife. Common in riverbeds and volcanic areas across the Western USA (e.g., Oregon, Idaho) and Madagascar. It often features 'conchoidal' (shell-like) fractures where chipped.

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