sedimentary
Tumbled Black Jasper
Silicon Dioxide (SiO2) with iron and carbon inclusions
Hardness: 6.5-7 on Mohs scale; Color: Deep black to charcoal grey; Luster: Vitreous to waxy (when polished); Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None; Specific Gravity: 2.58-2.91.
- Hardness
- 6
- Color
- Deep black to charcoal grey
- Luster
- Vitreous to waxy (when polished)
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Deep black to charcoal grey; Luster: Vitreous to waxy (when polished); Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None; Specific Gravity: 2.58-2.91.
Formation & geological history
Formed via the deposition of silica from water into cavities or cracks within other rocks, often associated with volcanic ash or sedimentary beds. The black color is typically derived from organic matter or iron-rich impurities.
Uses & applications
Primarily used for decorative purposes, jewelry (beads, cabochons), metaphysical practices, and as a component in lapidary art.
Geological facts
Black jasper is sometimes referred to as 'Basanite' and has historically been used as a touchstone to test the purity of gold and silver ores by observing the color of the streak left behind.
Field identification & locations
Identified in the field by its opaque nature, conchoidal fracture, and extreme hardness. It won't be scratched by a steel pocket knife. Found globally, notably in the USA, India, Russia, and Madagascar.
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