sedimentary

Chert (often called Jasper or Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Highly variable, featuring reds, yellows, and browns due to iron inclusions. Luster: Waxy to dull. Structure: Microcrystalline quartz. Fracture: Conchoidal (shell-like curves).

Hardness: 6
Luster: Waxy to dull

Identified July 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from aqueous fluids, often replacing organic material or occupying voids in limestone. It can form as nodules or bedded deposits and dates from various geological eras, including the Paleozoic.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges. Modernly used in lapidary work for jewelry, cabochons, and as decorative gravel.

Geological facts

Chert was one of the first materials utilized by early humans for tools because of its predictable fracture pattern. When it is red or yellow, it is commonly referred to in the lapidary trade as Jasper.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy luster, and curved, glass-like fracture surfaces. Frequently found in stream beds, gravel pits, and eroding out of limestone outcrops.

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