sedimentary

Chert with Iron Inclusions

Microcrystalline Quartz (SiO2) with Hematite/Limonite

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Tan, beige, or white base with reddish-brown jasper-like inclusions. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Luster: Waxy to dull

Identified July 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the precipitation of silica in sedimentary environments, often replacing organic material or filling cavities in limestone. The red spots are caused by iron oxide (hematite) impurities during formation.

Uses & applications

Primarily used for lapidary work as a decorative stone, historical use for stone tools (arrowheads) due to its sharp fracture, and as road ballast or aggregate in some regions.

Geological facts

Chert is so durable that it often survives long after the surrounding limestone has eroded away, which is why it is frequently found as rounded river pebbles or in gravel pits.

Field identification & locations

Identify by its hardness (it will scratch glass), waxy feel, and smooth curved (conchoidal) breaks. Red inclusions often indicate the transition into 'Jasper'. It is very common in glacial till and riverbeds across North America.