sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: dark grey to black with red jasper bands; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- dark grey to black with red jasper bands
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: dark grey to black with red jasper bands; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; typical of Precambrian to modern layers.
Uses & applications
Historically used for stone tools (knapping); modern uses include lapidary work, jewelry, and industrial abrasives.
Geological facts
Chert is so hard it can strike sparks from steel. Specimens with red banding are often referred to as Jasp-illite or banded iron formation depending on the iron content.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fractures and sharp edges. This specific banded variety is common in glacial tills and riverbeds in the Great Lakes region and various mountain ranges.
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