sedimentary
Chert with Calcite Veining
Microcrystalline Quartz (SiO2) with Calcium Carbonate (CaCO3) veins
Hardness: 7 (chert) / 3 (veins); Color: Black to dark grey matrix with white veins; Luster: Waxy to sub-vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 7 (chert) / 3 (veins)
- Color
- Black to dark grey matrix with white veins
- Luster
- Waxy to sub-vitreous
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Physical properties
Hardness: 7 (chert) / 3 (veins); Color: Black to dark grey matrix with white veins; Luster: Waxy to sub-vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed in marine sedimentary environments where silica-rich fluids replaced organic matter or limestone; the white veins formed later when tectonic stress cracked the rock and minerals (likely calcite or quartz) precipitated in the voids. Commonly found in the Zagros Mountains region of Iran.
Uses & applications
Historically used for stone tools due to sharp fracture edges; currently used for decorative garden stones, road aggregate, or as a specimen for geological study.
Geological facts
The region near Shiraz (the user's coordinates) part of the Zagros Fold-Thrust Belt, is famous for extensive sedimentary sequences where dark chert and limestone with secondary veining are extremely common.
Field identification & locations
Identify in the field by its hardness (chert will scratch steel) and its characteristic smooth, curved fracture surfaces. Calcite veins will fizz if touched with weak acid (vinegar).
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