sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale. Color: Tan, beige, or grey with a waxy luster. Crystal structure: Cryptocrystalline. Exhibits distinct conchoidal fracture with sharp edges. Opaque to translucent.

Hardness: 7 Mohs scale
Color: Tan, beige, or grey with a waxy luster

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale. Color: Tan, beige, or grey with a waxy luster. Crystal structure: Cryptocrystalline. Exhibits distinct conchoidal fracture with sharp edges. Opaque to translucent.

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) in sedimentary basins. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to sharp edges; currently used as construction aggregate, in road surfacing, and as flint for fire-starting.

Geological facts

Depending on its color and origin, it is also known as flint (darker varieties) or jasper (reddish). It is one of the most durable sedimentary rocks and often survives weathering better than surrounding limestone.

Field identification & locations

Identify in the field by its waxy appearance and the way it breaks into smooth, curved surfaces (conchoidal fracture). It will easily scratch glass and does not react with acid. Common in riverbeds and limestone outcrops.