sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Highly variable (grays, browns, reds due to iron oxides). Luster: Waxy to dull. Crystal structure: Cryptocrystalline (trigonal system). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Highly variable (grays, browns, reds due to iron oxides)
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Highly variable (grays, browns, reds due to iron oxides). Luster: Waxy to dull. Crystal structure: Cryptocrystalline (trigonal system). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in limestone or clay. This specific specimen shows typical conchoidal fracturing and iron staining common in nodules found in sedimentary basins.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Modern uses include abrasives, road construction aggregate, and semiprecious gemstones for jewelry when colorful.
Geological facts
Chert was one of the most important minerals for early humans, used to create fire and weaponry. It is so tough that it can often be found as rounded pebbles in stream beds long after the surrounding limestone has eroded away.
Field identification & locations
Identify in the field by its very smooth, seashell-like (conchoidal) fracture and its ability to scratch glass. It is commonly found in nodules within limestone or chalk beds. Look for a waxy texture and sharp-edged flakes.
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