sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brownish-red to mustard yellow (hematite/goethite inclusions); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brownish-red to mustard yellow (hematite/goethite inclusions); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms) or chemical precipitation from groundwater within sedimentary layers. These specimens appear to be stream-rounded pebbles.
Uses & applications
Historically used for stone tools due to sharp fracture edges; currently used for decorative stone, lapidary tumbling, and architectural gravel.
Geological facts
Chert has been used by humans for over 2 million years to create spear points and arrows. These specific specimens are commonly referred to as 'yellow jasper' or 'river jasper' when found in alluvial deposits.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), waxy feel, and smooth, curved (conchoidal) breaks. Found in riverbeds, gravel pits, and ancient sea beds globally.
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