sedimentary

Chert (Limestone-hosted Pebble)

Sedimentary Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Grey, blue-grey, yellowish-tan; Luster: Waxy to dull; Texture: Microcrystalline/Fine-grained; Fracture: Conchoidal; Specific Gravity: 2.6

Hardness: 6
Color: Grey, blue-grey, yellowish-tan
Luster: Waxy to dull

Identified June 11, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Grey, blue-grey, yellowish-tan; Luster: Waxy to dull; Texture: Microcrystalline/Fine-grained; Fracture: Conchoidal; Specific Gravity: 2.6

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation within limestone/chalk beds. This specific sample shows river or glacial smoothing, suggesting a Paleozoic era origin typically redistributed during the Pleistocene glaciations.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; modernly used as road aggregate or for lapidary tumbling.

Geological facts

Chert is so hard it can easily scratch glass and produces sparks when struck against steel. It is often found as nodules inside limestone or dolomite formations.

Field identification & locations

Identify by its waxy texture, durability, and the way it breaks in smooth curves (conchoidal fracture). Commonly found in Great Lakes glacial till, riverbeds, and limestone outcroppings.