sedimentary
Earthy Jasper (Chert)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-brown with mottled patterns; Luster: Dull to earthy (waxy when broken); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Brown, tan, and reddish-brown with mottled patterns
- Luster
- Dull to earthy (waxy when broken)
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Physical properties
Hardness: 6.5-7 Mohs; Color: Brown, tan, and reddish-brown with mottled patterns; Luster: Dull to earthy (waxy when broken); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed primarily through the precipitation of silica from groundwater or within sedimentary layers of ancient seafloors. The earthy brown color results from iron oxide (limonite or goethite) inclusions.
Uses & applications
Commonly used as a pocket stone, in decorative landscaping, or as a source material for lapidary work (tumbling and polishing). Historically used for knapping stone tools.
Geological facts
Jasper is a variety of chert. The name comes from the Greek word 'iaspis', meaning spotted stone. It is very resistant to erosion and is frequently found as rounded river or beach pebbles.
Field identification & locations
Identify by its high hardness (it will scratch glass) and lack of visible grains. It is commonly found in gravel pits, riverbeds, and glacial till throughout North America.
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