sedimentary
Chert (varietal Flint or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Gray, brown, and bluish-white. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Gray, brown, and bluish-white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Gray, brown, and bluish-white. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids within limestone or chalk beds. Can range from Precambrian to Holocene in age.
Uses & applications
Used historically for stone tools and weapons due to sharp edges; currently used for road surfacing, lapidary gemstones, and primitive fire-starting (flint and steel).
Geological facts
Because it breaks with a conchoidal fracture, it produces edges that can be sharper than a surgical scalpel. It is one of the most common materials used for prehistoric arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and bowl-shaped (conchoidal) chips or fractures. Commonly found in riverbeds or as nodules within limestone outcrops.
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