sedimentary
Chert (Jasper/Agate variety)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan with dark inclusions; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Brownish-tan with dark inclusions
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brownish-tan with dark inclusions; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation within sedimentary rock layers, often occurring as nodules in limestone or chalk beds. This specimen appears water-worn, suggesting transport in a river or stream.
Uses & applications
Common varieties are used in construction aggregate and landscaping; high-quality colorful specimens are used as gemstones (lapidary), jewelry, and for making stone tools (flintknapping) due to its sharp edges.
Geological facts
Chert was one of the most important minerals for early humans, used to create arrowheads, scrapers, and knives. Because it consists of microscopic quartz crystals, it is extremely durable and resistant to chemical weathering.
Field identification & locations
Identify in the field by checking for a waxy texture and conchoidal (shell-like) fracture patterns when chipped. It is harder than steel and will scratch a glass bottle. Common in riverbeds, glacial till, and sedimentary outcrops globally.
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