sedimentary
Chert (Yellow Jasper variant)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5–7 on Mohs scale. Color: Opaque mustard yellow due to iron oxide (goethite) inclusions. Luster: Dull to waxy. Crystal Structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.7.
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Opaque mustard yellow due to iron oxide (goethite) inclusions. Luster: Dull to waxy. Crystal Structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.7.
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids in sedimentary basins. This specimen likely dates from the Cretaceous or older.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for lapidary work, decorative landscaping, and as a gemstone for jewelry (beads, cabochons).
Geological facts
Yellow jasper is known as a stone of protection and was often used by ancient civilizations for amulets. It is basically a highly impure, opaque form of chalcedony.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture, extreme hardness (will scratch glass), and opaque yellow-brown cortex. Commonly found in riverbeds or as nodules within limestone/chalk.
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