sedimentary
Microcrystalline Quartz (Chert/Agate)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, yellowish-white; Luster: Waxy to vitreous; Crystal structure: Hexagonal (trigonal); Fracture: Conchoidal; Specific gravity: approx 2.6
- Hardness
- 6
- Color
- Cream, tan, yellowish-white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, yellowish-white; Luster: Waxy to vitreous; Crystal structure: Hexagonal (trigonal); Fracture: Conchoidal; Specific gravity: approx 2.6
Formation & geological history
Formed via the accumulation of silica-rich fluids in sedimentary rock cavities or the replacement of organic material. These specimens are often millions of years old, weathered by water and erosion into smooth nodules.
Uses & applications
Commonly used as decorative stones, in lapidary work for tumbling, and historically as the primary material for stone tools (arrowheads) due to its sharp conchoidal fracture.
Geological facts
In its many forms, microcrystalline quartz is one of the most common materials on Earth's crust. When it is translucent and banded, it is called agate; when opaque and dull, it is called chert or jasper.
Field identification & locations
Can be identified by its smooth, waxy feel and its ability to scratch glass. Found widely in riverbeds, glacial tills, and coastal areas across the globe. Smooth specimens like this are often referred to as 'river stones.'
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