sedimentary
Jasper or Agate-bearing Chert
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 6.5-7 on Mohs scale. Color: Mottled grey, white, and reddish-brown. Luster: Waxy to vitreous. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.
- Hardness
- 6
- Color
- Mottled grey, white, and reddish-brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Mottled grey, white, and reddish-brown. Luster: Waxy to vitreous. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in volcanic or sedimentary environments. Most specimens can range from millions to over a billion years old.
Uses & applications
Commonly used for lapidary work (cabochons and beads), decorative stones, aquarium gravel, and historical tool-making (flintknapping).
Geological facts
This specimen shows the transition between common chert and jasper. The reddish streaks are caused by iron oxide (Hematite) impurities. Historically, these silica-rich stones were the primary materials for prehistoric arrowheads and scrapers due to their predictable fracturing.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in river beds, beaches, and sedimentary outcrops worldwide, particularly in glacial till or areas with volcanic history.
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