sedimentary

Chert (Brown Variety)

Silicon dioxide (SiO2)

Hardness: 7 on Mohs scale. Color: Brown, tan, or dark chocolate. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None; exhibits prominent conchoidal (shell-like) fracture. Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, or dark chocolate
Luster: Waxy to vitreous

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in saltwater environments. It can also form as nodules in limestone or chalk beds. Its geological age ranges from Precambrian to Holocene.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp fracture edges. Today it is used as road surfacing material, in some types of glass manufacturing, and as a semi-precious gemstone for jewelry (cabochons) when attractively patterned.

Geological facts

Darker varieties are often called flint. It is extremely durable and chemically stable, allowing it to survive long-term weathering. It was one of the first materials used by early humans for fire-starting and weaponry.

Field identification & locations

Identify in the field by its smooth, shell-like fracture surfaces and the fact that it can scratch glass. It is common in riverbeds, glacial till, and embedded in limestone outcrops. Collectors look for pieces with unique banding or 'leopard' spots.