sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs); Color: Tanish-brown/honey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture)
- Hardness
- 6
- Color
- Tanish-brown/honey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Tanish-brown/honey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture)
Formation & geological history
Forms primarily as a biochemical sedimentary rock by the accumulation of siliceous remains or as a chemical precipitate replacing limestone or dolostone. Common in prehistoric seafloor deposits.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; used today as a decorative stone and in landscaping.
Geological facts
This specimen displays a distinct conchoidal (shell-like) fracture pattern, which is why it was the primary material for arrowheads and scrapers during the Stone Age.
Field identification & locations
Identified in the field by its hardness (cannot be scratched by a steel nail), waxy luster, and smooth, curved fracture surfaces. Found worldwide in nodules or bedded layers.
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