sedimentary
Chert (Jasper variation)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Brownish-red to chocolate brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Brownish-red to chocolate brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Brownish-red to chocolate brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich microfossils or chemical precipitation of silica in marine environments, subsequently hardening over millions of years. This specimen shows significant tumbling/rounding, likely from river or beach action.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for lapidary work, landscaping, and gemstone collecting.
Geological facts
Chert is so durable that it can survive long periods of environmental transport. The specific brown/red colors are usually caused by inclusions of iron oxides.
Field identification & locations
Identified by its extreme hardness (will scratch glass), waxy luster, and conchoidal (shell-like) fracture patterns. Often found in gravel beds or eroded out of limestone formations.
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