sedimentary
Chert / Flint
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, or cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, or cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, or cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (exhibits conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation from groundwater within limestone or chalk beds. Typically found in Paleozoic or Mesozoic age strata.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road surfacing, architectural stone, and as a component in ceramics.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its extensive use in flintlock firearms. The specimen in the image shows distinct conchoidal (shell-like) fracturing on the edges, which is a hallmark of high-silica stones.
Field identification & locations
Identify in the field by its hardness (it will scratch glass and metal), smooth waxy feel, and glass-like curved fractures. Commonly found as nodules or layers within sedimentary basins globally.
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