sedimentary
Chert (Limestone-hosted Pebble)
Sedimentary Cryptocrystalline Quartz (SiO2)
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
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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.
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