sedimentary
Chert Nodule
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale. Color: Tan, beige, or grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 Mohs scale
- Color
- Tan, beige, or grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale. Color: Tan, beige, or grey. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica within sedimentary rock layers, often limestone or chalk, through chemical replacement. Commonly found in Mesozoic or Paleozoic marine deposits.
Uses & applications
Used historically for stone tools (arrowheads). Modernly used in construction aggregate, road base, and as decorative landscape stone. Higher quality varieties like jasper/agate used in jewelry.
Geological facts
Small nodules with natural holes are sometimes called 'hag stones' or 'fairy stones' in folklore. Chert is one of the most durable sedimentary materials and has been used by humans for millions of years.
Field identification & locations
Identify by its waxy luster, extreme hardness (it will scratch glass), and conchoidal fracture. Often found as rounded pebbles in riverbeds or within limestone outcrops.
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