sedimentary
Chert (Jasper)
Microcrystalline Quartz (SiO2) with iron oxide inclusions
Hardness: 7 (Mohs scale); Color: Red-brown to orange-tan due to iron staining; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- Red-brown to orange-tan due to iron staining
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Red-brown to orange-tan due to iron staining; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed primarily from the precipitation of silica in sedimentary environments, often through the accumulation of siliceous organisms like diatoms or radiolarians, or via chemical replacement in limestone. The reddish hue indicates oxidation of iron during formation.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges; modernly used in landscaping, as semi-precious gemstones in jewelry (lapidary), and as a decorative building stone.
Geological facts
Jasper and Chert are varieties of chalcedony. Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was one of the most important minerals for early humans to create cutting tools.
Field identification & locations
Identify in the field by its waxy luster, lack of visible crystals, and its ability to scratch glass. It often occurs as nodules in sedimentary rocks or as pebbles in stream beds. Common in iron-rich geological regions.
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