sedimentary

Chert (Tan/Buff variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, buff, or grayish-white; Luster: Waxy to dull; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, buff, or grayish-white
Luster: Waxy to dull

Identified May 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, buff, or grayish-white; Luster: Waxy to dull; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich marine organisms or by chemical precipitation of silica from groundwater replacing limestone or chalk. Commonly found in Paleozoic or Mesozoic sedimentary beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to conchoidal fracture. Modernly used in road construction, as an abrasive, and occasionally in inexpensive jewelry or lapidary art.

Geological facts

Chert is so hard that it can strike sparks from steel, which led to its historical use as 'flint' in firearms. It is incredibly durable and can survive millions of years of weathering.

Field identification & locations

Identify in the field by its waxy texture, sharp edges, and unique 'U' shaped (conchoidal) fractures. It will easily scratch glass and will not react with acid, unlike the limestone it is often found within.