sedimentary
Chert / Jasper
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Greenish-brown, tan, and earthy tones. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Greenish-brown, tan, and earthy tones
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Greenish-brown, tan, and earthy tones. Luster: Waxy to dull. Crystal Structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical replacement of limestone/dolomite by silica-rich fluids. Can be of various geological ages from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp fracture edges. Today used as aquarium gravel, landscaping stone, and occasionally in lapidary work for cabochons.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. Jasper is the name specifically given to opaque, impure varieties of chert often colored by iron oxides.
Field identification & locations
Identify in the field by its hardness (it should scratch glass), its waxy feel, and its curved, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial till, and embedded in limestone outcrops.
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