sedimentary
Chert (Jasper/Agate variant)
Microcrystalline Quartz (SiO2) with iron oxide inclusions
Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, ochre, and olive green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 6
- Color
- Tan, brown, ochre, and olive green
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, ochre, and olive green; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed via the accumulation of silica-rich fluids within sedimentary host rocks or volcanic cavities. This specimen likely formed through the replacement of limestone or as a secondary precipitate in volcanic gas bubbles.
Uses & applications
Used historically for stone tools due to its sharp edges when fractured. Currently used for lapidary work, jewelry (tumbled stones), and as a landscape aggregate.
Geological facts
This specimen displays a waxy luster and translucent edges characteristic of chalcedony. The yellow-brown staining is caused by limonite or goethite (iron) impurities.
Field identification & locations
Identified by its conchoidal (shell-like) fracture, waxy surface, and inability to be scratched by a steel knife. Common in riverbeds and gravel pits. Collectors look for translucent 'windows' when held to light.
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