sedimentary
Chert (Yellow Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scaled); Color: Dull yellowish-brown to tan with darker dendritic or spotted inclusions; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs scaled); Color: Dull yellowish-brown to tan with darker dendritic or spotted inclusions; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed via the accumulation of silica-rich microfossils (like radiolarians) or chemical precipitation in marine or groundwater environments. This specimen appears water-worn, likely from a river or beach setting.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Modern uses include tumbling for decorative 'river rocks,' lapidary work for jewelry, and as an industrial abrasive.
Geological facts
Yellow jasper is essentially a variety of chert colored by iron hydroxide impurities (like goethite). It was highly valued by early humans for making scrapers and arrowheads because of its predictable fracture pattern.
Field identification & locations
Identified in the field by its hardness (it will scratch glass), its smooth, waxy surface when wet, and its characteristic curved (conchoidal) breaks. Often found in riverbeds or landscaping gravel.
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