sedimentary

Chert (Light Grey / Flint variant)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Light grey to white; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Trigonal; Fracture: Conchoidal; Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Light grey to white
Luster: Dull to waxy

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Light grey to white; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Trigonal; Fracture: Conchoidal; Specific Gravity: 2.65

Formation & geological history

Forms through the precipitation of silica in marine environments, often replacing organic matter or limestone. It can also form as primary chemical precipitates from hydrothermal fluids or silica-rich deep-sea ooze.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used as road aggregate, in glass manufacturing, and as a low-cost gemstone for lapidary work.

Geological facts

Chert is so hard it will scratch steel. It is nearly identical in composition to quartz but has a much finer grain, making it opaque rather than transparent. It was the most important material for Neolithic societies making arrowheads and spear points.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Found worldwide in sedimentary basins, often as nodules inside limestone or chalk beds.