sedimentary
Chert (Jasper/Agate mix)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tan, brown, white, and earthy tones; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
- Hardness
- 6
- Color
- Tan, brown, white, and earthy tones
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tan, brown, white, and earthy tones; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich fluids in limestone or through the diagenetic replacement of existing sediments. Often found in seafloor deposits or volcanic ash beds.
Uses & applications
Historically used for making sharp tools like arrowheads. Modernly used as decorative landscape stone, in tumbled jewelry, and for lapidary hobbies.
Geological facts
Chert is so hard it can strike sparks against steel. This specific specimen shows banded chalcedony (agate) and opaque chert/jasper typical of river-worn gravels.
Field identification & locations
Identify by its 'glassy' waxy texture and shell-like (conchoidal) fractures. Found worldwide in creek beds, gravel pits, and sedimentary rock formations like the Great Lakes region or the Mississippi River valley.
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