sedimentary

Chert (Flint/Chalcedony)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs; Color: Brown, tan, and gray; Luster: Waxy to vitreous; Structure: Microcrystalline (cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Brown, tan, and gray
Luster: Waxy to vitreous

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brown, tan, and gray; Luster: Waxy to vitreous; Structure: Microcrystalline (cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica from groundwater filling cavities in limestone or chalk, or from the accumulation of siliceous remains of marine organisms. Commonly found in Paleozoic and Mesozoic sedimentary strata.

Uses & applications

Historically used for stone tools (arrowheads/knives) and fire-starting. Currently used in jewelry as lapidary material, road surfacing, and as a component in glass and ceramics manufacturing.

Geological facts

This specimen shows the characteristic waxy luster and sharp, shell-like (conchoidal) fractures that made it the primary material for prehistoric tool making. It is essentially a non-banded form of chalcedony.

Field identification & locations

Identify by its ability to scratch glass and its sharp, curved fracture edges. Commonly found in riverbeds, fields, or within limestone outcrops. Collectors look for vibrant colors or translucent edges.