sedimentary
Chert (Iron-stained)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, ochre (due to iron oxidation), gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, ochre (due to iron oxidation), gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, ochre (due to iron oxidation), gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal; Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organisms (like radiolarians or diatoms) or chemical precipitation in marine or groundwater environments. This specimen shows significant weathering and iron oxide staining from long-term exposure to water and air.
Uses & applications
Historically used for stone tools and weapons (flint-knapping); currently used as a common construction aggregate, landscaping stone, and in some decorative lapidary work.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most important minerals for early human civilizations to create sharp edges for hunting and survival.
Field identification & locations
Identify in the field by its very hard, smooth texture, waxy luster, and conchoidal (shell-like) fractures. It will not react with acid. Commonly found in limestone or chalk beds as nodules or layers.
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