sedimentary
Chert (Jasper/Flint variant)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Opaque tan, yellow, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Opaque tan, yellow, and brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Opaque tan, yellow, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. Often occurs as nodules in limestone or chalk beds. This specimen appears consistent with formations found in the Mesozoic or Cenozoic eras.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges. Currently used as an industrial abrasive, in road construction, and as decorative gravel. Higher-quality colorful specimens are used for lapidary work like cabochons.
Geological facts
Chert was one of the most important minerals to prehistoric humans; its ability to shatter into razor-sharp flakes made it the primary material for arrowheads and knives. It is chemically identical to quartz but contains impurities that provide its color and opacity.
Field identification & locations
Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It often feels slightly greasy or waxy to the touch. Commonly found in riverbeds, glacial till, and sedimentary outcrops globally.
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