sedimentary

Chert Breccia

Brecciated Chert (Sedimentary Rock)

Hardness: 6.5-7 Mohs. Color: Multi-colored with tan, brown, orange, and grey. Luster: Waxy to vitreous. Structure: Clastic with angular rock fragments. Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Multi-colored with tan, brown, orange, and grey
Luster: Waxy to vitreous

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the mechanical fracturing of existing chert or jasper beds, followed by the deposition of a fine-grained mineral cement (often silica) that binds the angular fragments together. This typically occurs in high-energy sedimentary environments or along fault zones.

Uses & applications

Primarily used as decorative stone, aquarium gravel, or lapidary material for polishing. Historically, high-silica versions like this were used for stone tool making.

Geological facts

Unlike conglomerate, which has rounded edges from water transport, breccia features sharp, angular fragments, indicating the material did not travel far after breaking.

Field identification & locations

Identify by looking for angular, broken fragments of jasper or chert encased in a solid matrix. Common in riverbeds, glacial till, and around fault lines where seismic activity breaks rock.

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Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Sandstone

Arenite (primarily SiO2)

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