sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or opaque white; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, or opaque white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, or opaque white; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical precipitation of silica in groundwater. Often found in nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to its sharp conchoidal fracture. Today used in construction (road metal), as gemstones (Jasper varieties), and in flint-knapping craft.
Geological facts
Chert has been used by humans for over 2 million years to create tools. The reddish tint specifically seen in many specimens is often caused by iron oxide impurities.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth 'waxy' texture, and its shell-like (conchoidal) breaking pattern. Common in riverbeds and limestone outcrops.
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