sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with a waxy luster; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, brown with a waxy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, brown with a waxy luster; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed via the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation from silica-rich fluids in sedimentary basins. This specimen has been rounded by fluvial (river) erosion.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; currently used as construction aggregate, road base, and decorative landscaping stones.
Geological facts
Chert is essentially the same material as flint, but the term 'flint' is often reserved for dark chert found in chalk or limestone. It is one of the most durable rocks on the Earth's surface.
Field identification & locations
Identified in the field by its hardness (will scratch glass), waxy to dull luster, and smooth, rounded shape if found in water. It often shows 'conchoidal' fractures that look like curved shell patterns.
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