sedimentary
Chert (specifically Chalcedony/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, white, and reddish-pink patches; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, white, and reddish-pink patches
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, white, and reddish-pink patches; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite by silica-rich fluids. This specimen appears to be a 'nodule' or fragment common in sedimentary strata ranging from the Paleozoic to Cenozoic eras.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; modernly used as high-end construction aggregate, in lapidary work for jewelry (cabochons), and for fire-starting strikers.
Geological facts
Chert was one of the most vital resources for prehistoric humans because it breaks with a conchoidal fracture, creating edges sharper than a steel scalpel. High-quality colorful chert is often referred to as jasper or agate.
Field identification & locations
Identify in the field by its waxy texture, smooth conchoidal (shell-like) fracture surfaces, and extreme hardness (it will easily scratch glass and steel). Commonly found in limestone beds or as gravel in stream beds.
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