sedimentary
Red Jasper (Ocherous Chert)
Silicon Dioxide (SiO2) with Hematite impurities
Hardness: 6.5-7 (Mohs scale); Color: Brick red to brownish-red; Luster: Dull or waxy when unpolished; Crystal Structure: Microcrystalline (trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.9.
- Hardness
- 6
- Color
- Brick red to brownish-red
- Luster
- Dull or waxy when unpolished
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brick red to brownish-red; Luster: Dull or waxy when unpolished; Crystal Structure: Microcrystalline (trigonal); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.9.
Formation & geological history
Usually forms from the deposition of silica in hydrothermal veins or via the accumulation of radiolarian tests in sedimentary environments. The red color comes from iron oxide (hematite) inclusions incorporated during formation.
Uses & applications
Commonly used in jewelry (cabochons, beads), decorative lapidary arts, and as a semi-precious gemstone. Historically used for seal stones and tools due to its hardness.
Geological facts
Jasper has been used as a gemstone since antiquity and is mentioned in various historical texts. The name comes from the Greek word 'iaspis', meaning 'spotted stone'. It is a variety of chalcedony.
Field identification & locations
Identified in the field by its distinct opaque red color, significant hardness (it will scratch glass), and smooth, shell-like (conchoidal) fracture pattern. Found globally, often in volcanic or sedimentary gravels.
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