sedimentary
Chert (varieties: Flint or Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Brown, tan, or grey with a waxy to dull luster. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits sharp conchoidal (shell-like) fracture. Specific Gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Brown, tan, or grey with a waxy to dull luster
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Physical properties
Hardness: 7 on the Mohs scale. Color: Brown, tan, or grey with a waxy to dull luster. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits sharp conchoidal (shell-like) fracture. Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica from groundwater within limestone or chalk beds. Occurs across all geological ages, notably in Cretaceous chalk deposits.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a component in ceramics or as a flint-striker for survival gear.
Geological facts
Chert was one of the most important minerals to prehistoric humans. Known as 'nature's glass', it was the primary material for the Stone Age technology revolution. It is so chemically stable that it can survive billions of years in the geological record.
Field identification & locations
Identify in the field by its waxy texture and distinctive shell-like curved fractures when broken. Commonly found as nodules in limestone or as pebbles in riverbeds and beaches. Collectors look for translucent edges and unique color banding.
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