sedimentary
Chert (Jasper/Agate Peat)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and tan; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Red, brown, and tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Red, brown, and tan; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or through the chemical replacement of host rocks. These specific water-worn pebbles are often found in river beds or glacial till.
Uses & applications
Used historically for stone tools due to sharp edges when fractured; modernly used in jewelry (as semi-precious gemstones), rock tumbling, and as decorative landscape gravel.
Geological facts
Chert and its varieties like Jasper have been used since the Stone Age to create spearheads and arrowheads because they break with a predictable, razor-sharp edge.
Field identification & locations
Identified by its smoothness, conchoidal fracture (curved surfaces), and hardness. Often found in riverbeds or beaches as rounded 'river rocks'.
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