sedimentary

Chert (Limestone Nodule)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohsscale); Color: light greyish-tan; Luster: dull to waxy; Structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 6
Color: light greyish-tan
Luster: dull to waxy

Identified July 10, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohsscale); Color: light greyish-tan; Luster: dull to waxy; Structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. Often found as nodules within limestone or chalk beds. Geological age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and arrowheads; currently used in construction aggregate, roads, and as aquarium or decorative stones.

Geological facts

Chert was a primary material for prehistoric toolmaking due to its ability to fracture with extremely sharp edges. It is chemically similar to quartz but with a much finer crystalline structure.

Field identification & locations

Identify by its hardness (it will scratch glass), its smooth, rounded river-worn texture, and its waxy luster when broken. It is commonly found in riverbeds and limestone outcrops globally.