sedimentary (microcrystalline quartz)
Black Jasper (Black Onyx substitute)
Silicon Dioxide (SiO2) with carbonaceous impurities
Hardness: 6.5–7 on Mohs scale; Color: Opaque black; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
- Hardness
- 6
- Color
- Opaque black
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Opaque black; Luster: Vitreous to waxy; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
Formation & geological history
Formed through the deposition of silica-rich fluids in volcanic or sedimentary rock cavities. The black color is usually due to the inclusion of organic matter or iron oxides during the silicification process.
Uses & applications
Primarily used in jewelry as cabochons for rings and pendants, as well as for decorative carvings, worry stones, and metaphysical purposes.
Geological facts
Black Jasper, sometimes called 'Basanite' when used as a touchstone, has been used since antiquity to test the purity of gold and silver by observing the color of the streak left on the stone's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its opaque nature (it does not let light through even at the edges). It is commonly found in riverbeds or volcanic regions in India, Brazil, and the USA.
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