sedimentary
Chert (Flint / Quartz Nodule)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Brownish-grey with a light, weathered outer cortex or rind. Luster: Waxy to dull. Fracture: Conchoidal (produces sharp edges). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brownish-grey with a light, weathered outer cortex or rind
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Brownish-grey with a light, weathered outer cortex or rind. Luster: Waxy to dull. Fracture: Conchoidal (produces sharp edges). Specific Gravity: 2.65.
Formation & geological history
Formed through sedimentary processes, often as nodules or concretions in limestone and chalk beds, where silica precipitates from seawater or pore fluids.
Uses & applications
Historically used for making stone tools (arrowheads, blades) and striking fire. Today used primarily in road construction aggregate, lapidary art, and as decorative stone.
Geological facts
Chert breaks with extremely sharp edges, which allowed prehistoric humans to craft some of the earliest cutting tools and projectile points in human history.
Field identification & locations
Identify in the field by its hardness (scratches glass readily), smooth conchoidal fracture surfaces, and distinct chalky or weathered outer cortex. Found abundantly worldwide in marine sedimentary rock layers.
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