sedimentary
Jasper Shard / Chert
Silicon dioxide (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Variegated brown, tan, and dark gray; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9
- Hardness
- 6
- Color
- Variegated brown, tan, and dark gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Variegated brown, tan, and dark gray; Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9
Formation & geological history
Formed from the accumulation of silica-rich micro-organisms (like radiolaria) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in ancient ocean beds and volcanic ash deposits.
Uses & applications
Commonly used as a semi-precious gemstone in jewelry (when polished), lapidary art, knapping tools (historically for arrowheads), and as decorative gravel.
Geological facts
Jasper is an opaque variety of chalcedony. It has been used by humans since Neolithic times to create sharp tools because of its conchoidal fracturing properties. The variations in color are caused by mineral impurities like iron oxides.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth 'glass-like' fracture surfaces, and its opacity. Common in river beds and desert regions worldwide.
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