sedimentary
Chert (with Iron Staining)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, and red (from iron oxides); Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Tan, brown, and red (from iron oxides)
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, and red (from iron oxides); Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms or by chemical precipitation in groundwater; typically found in limestone or dolomite formations.
Uses & applications
Historically used for stone tools due to its sharp edges; today used as aggregate in road construction and occasionally as an ornamental stone or for lapidary work.
Geological facts
The red coloring is known as iron staining and occurs when iron-rich minerals like hematite or goethite weather on the rock's surface. High-quality varieties are often called Jasper.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture patterns. Found globally in sedimentary basins.
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