sedimentary
Chert (Arrowhead Shard)
Microcrystalline silica (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, black, and tan mottled; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6
- Hardness
- 7 (Mohs scale)
- Color
- Gray, black, and tan mottled
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, black, and tan mottled; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. This specific piece shows evidence of anthropogenic knapping (flake scars), indicating it was worked by humans.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as a decorative stone or for industrial abrasives and road surfacing.
Geological facts
Chert was one of the first materials used by early humans to create survival tools. It sparks when struck against steel, which also made it a key component in flintlock firearms.
Field identification & locations
Identifiable by its conchoidal (shell-like) fracture edges and waxy texture. Frequently found in limestone or chalk deposits. Collectors should look for 'flake' scars indicating human manipulation.
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