sedimentary
Chert (with Quartz Druzy)
Microcrystalline Silica (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen shows secondary quartz crystallization (druzy) in a vug or cavity.
Uses & applications
Used historically for stone tools due to its conchoidal fracture; currently used in construction aggregate, as a gemstone (jaspers), and as collector specimens.
Geological facts
Chert is one of the most durable sedimentary rocks and often preserves microfossils. High-quality varieties like flint were the primary technological material for early humans.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife), waxy luster, and smooth, curved fracture surfaces. Commonly found in limestone or chalk beds.
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