sedimentary
Quartz (Agate or Chert pebble)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and translucent orange; Luster: Waxy to vitreous; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: approx. 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and translucent orange
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and translucent orange; Luster: Waxy to vitreous; Crystal structure: Hexagonal (cryptocrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: approx. 2.65
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of igneous rocks or as nodules in sedimentary limestone or chalk. Often smoothed into pebbles by water erosion in riverbeds or beaches.
Uses & applications
Common varieties are used for landscape decor, tumbled stones for jewelry, and microcrystalline versions are used in making glass and abrasive tools.
Geological facts
Agates and microcrystalline quartz have been used by humans for millions of years to create sharp tools and weapons due to their conchoidal fracture pattern.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and waxy luster. Commonly found in riverbeds, glacial till, and gravel pits globally.
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