sedimentary
Chert Breccia
Microcrystalline Quartz (SiO2) Breccia
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7. It features angular rock fragments cemented by a fine-grained matrix.
- Hardness
- 7 (Mohs scale)
- Color
- Variegated brown, tan, and grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Variegated brown, tan, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7. It features angular rock fragments cemented by a fine-grained matrix.
Formation & geological history
Formed through the brittle fracturing of chert beds followed by the precipitation of silica or carbonate minerals that cement the angular fragments together. This typically occurs in high-energy sedimentary environments or near fault zones.
Uses & applications
Primarily used as a decorative stone in landscaping, for study in educational geology collections, and historically for stone tool making due to its conchoidal fracture which provides sharp edges.
Geological facts
Chert is essentially the same mineral as jasper and flint. Because it is so hard and chemically stable, it often survives long-distance transport in rivers and is commonly found in gravel pits far from its original source.
Field identification & locations
Identify in the field by its hardness (will scratch glass), angular clasts, and waxy luster on fresh breaks. Look for it in river beds, glacial till, or sedimentary basins where limestone or chert outcrops are present.
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