sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, with dark inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 6
- Color
- Tan, brown, with dark inclusions
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, with dark inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Forms primarily as nodules or beds in sedimentary rocks through the accumulation of silica-rich fluids or organic remains (like diatoms/radiolarians) that recrystallize over millions of years. Common in limestone and dolostone formations.
Uses & applications
Historically used for stone tools and arrowheads; currently used as decorative gravel, in lapidary work (jewelry), and for building materials. High quality specimens are sought by mineral collectors.
Geological facts
Chert is so hard it can create sparks when struck against steel, which made it a vital survival tool for early humans. It is chemically identical to quartz but has a different internal structure.
Field identification & locations
Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern. Look for it in riverbeds or within limestone outcrops. It will scratch glass easily.
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