sedimentary
Chert (Jasper influence)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and red (from iron oxides); Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and red (from iron oxides)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and red (from iron oxides); Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. The reddish hues suggest secondary iron oxide staining. Common in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; commercially used as an abrasive, in road surfacing, or as lapidary material for jewelry as jasper.
Geological facts
Chert is one of the most durable rocks and has been used by humans for millions of years to create arrowheads and scrapers. The reddish-brown variety is often referred specifically as Jasper.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), conchoidal (shell-like) fracture, and smooth, waxy texture on broken surfaces. Often found as nodules or 'potstones' in limestone regions.
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