sedimentary
Chert (or Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Brown, tan, reddish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: Brown, tan, reddish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater filling pores in sedimentary rocks or from the accumulation of siliceous remains of marine organisms. Commonly found in limestone or dolomite formations.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as decorative landscaping rocks, in construction aggregate, and occasionally for jewelry if it possesses unique patterns.
Geological facts
Small pieces of chert like this are often called 'river rocks' or 'flint' and were often the primary source material for prehistoric tools due to their predictable fracturing and sharpness.
Field identification & locations
Identified in the field by its waxy luster, extreme hardness (it will scratch glass), and its shell-like (conchoidal) fracture pattern. Found globally in riverbeds and sedimentary outcrops.
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