sedimentary

Chert (with Iron Staining)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified June 27, 2026More sedimentary →

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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.