sedimentary

Chert (Chalcedony/Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale; Color: Gray, tan, brown, and translucent cream; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: Gray, tan, brown, and translucent cream
Luster: Waxy to vitreous

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the accumulation of silica-rich microfossils (like radiolaria or diatoms) or through the chemical precipitation of silica in groundwater within sedimentary host rocks. Common in limestone or dolostone formations.

Uses & applications

Used historically for stone tools (knapping) due to its sharp edges; modern uses include aggregate in construction, abrasives, and as semi-precious lapidary material for jewelry and cabochons.

Geological facts

Chert has been used by humans for over two million years to create tools. Flint is a variety of chert often associated with chalk or marly limestone. When struck against steel, chert can produce sparks, leading to its historical use in flintlock firearms.

Field identification & locations

Field identification involves looking for a waxy luster, conchoidal (shell-like) fracture patterns, and testing for high hardness (it will scratch glass). It is often found as nodules or layers within sedimentary rock outcrops.