sedimentary

Chert (Iron-stained)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Tan/yellowish-brown due to limonite/iron oxide staining; Luster: Waxy to dull; Structure: Non-crystalline mass (microscopic trigonal crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan/yellowish-brown due to limonite/iron oxide staining
Luster: Waxy to dull

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine or groundwater environments. This specimen appears weathered and rolled, likely from a fluvial or glacial deposit.

Uses & applications

Historically used for stone tools (flintknapping); industrially used as an abrasive or aggregate; commonly used in landscaping and road base construction.

Geological facts

Chert is so durable it can survive billions of years of erosion. Iron-stained varieties are often found in riverbeds where they pick up mineral pigments from surrounding water and soil.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and metal) and its characteristic smooth, bowl-shaped conchoidal fractures. It is found globally, particularly in limestone and chalk deposits.

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