sedimentary
Black Jasper
Silicon dioxide (SiO2) with carbon/mineral inclusions
Hardness: 6.5-7 (Mohs scale); Color: Black with green/grey mottling; Luster: Vitreous to waxy (when polished); Structure: Microcrystalline (trigonal); Cleavage: None; Opaque.
- Hardness
- 6
- Color
- Black with green/grey mottling
- Luster
- Vitreous to waxy (when polished)
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Black with green/grey mottling; Luster: Vitreous to waxy (when polished); Structure: Microcrystalline (trigonal); Cleavage: None; Opaque.
Formation & geological history
Formed through the deposition of silica-rich fluids in volcanic or sedimentary environments, often darkening due to the presence of carbon or iron-rich minerals during the consolidation process.
Uses & applications
Primarily used for lapidary work, jewelry (beads, cabochons), tumbled stones for collecting, and metaphysical ornamental pieces.
Geological facts
Black Jasper is sometimes called 'Blackstone' or 'Basanite' in historical gemstone contexts and was famously used by ancient civilizations as a touchstone to test the purity of gold and silver.
Field identification & locations
Identify by its high hardness (won't scratch with a copper penny or steel knife), smooth conchoidal fracture, and absolute opacity even when held to a strong light. Commonly found in riverbeds or coastal deposits.
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