sedimentary
Chert (Jasper/Agate variety)
Microcrystalline quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, and creamy white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation from hydrothermal fluids in volcanic or sedimentary environments. Often found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (arrowheads) due to its sharp edges. Currently used as an ornamental stone, for lapidary work (jewelry), and as a collector's specimen.
Geological facts
Because of its high hardness and conchoidal fracture pattern, chert was one of the most important materials for early humans to create survival tools. Varieties with bright colors like this specimen are often called Jasper.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to easily scratch glass. Common in desert and mountain environments across the American Southwest.
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