sedimentary
Chert (Jasper variation)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Reddish-brown, tan, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich biogenic material or by the replacement of carbonate minerals with silica in sedimentary environments. Common in marine and lacustrine deposits.
Uses & applications
Historically used for stone tools (knapping); modernly used for lapidary work, jewelry (beads and cabochons), and as a decorative stone.
Geological facts
Chert has a conchoidal fracture which allows it to break into sharp edges, making it the primary material for prehistoric arrowheads and scrapers. Jasper is a variety of chert colored by iron oxides.
Field identification & locations
Identify in the field by its hardness (it can scratch glass), waxy luster, and shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or as nodules in limestone.
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