sedimentary
Chert (Jasper variation)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: reddish-brown, tan, and gray; Luster: waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- reddish-brown, tan, and gray
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: reddish-brown, tan, and gray; Luster: waxy to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Forms through the chemical precipitation of silica-rich fluids or the accumulation of siliceous skeletal remains (like radiolarians) in deep-sea environments, eventually hardening into microcrystalline quartz.
Uses & applications
Historically used for stone tools and arrowheads due to its sharp edges; currently used for lapidary work, jewelry, and as aquarium or decorative landscape stone.
Geological facts
This specimen shows the classic 'conchoidal' fracture pattern, meaning it breaks with smooth, curved surfaces similar to glass. This property made it essential for prehistoric humans to create sharp cutting tools.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its waxy feel, and the way it breaks into sharp, shell-like curves. Common in riverbeds and limestone formations.
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