sedimentary
Black Jasper
Silicon Dioxide (SiO2) with inclusions
Hardness: 6.5-7 (Mohs scale), Color: Jet black to dark charcoal, Luster: Vitreous to sub-vitreous, Crystal structure: Hexagonal (Microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6 - 2.9
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Jet black to dark charcoal, Luster: Vitreous to sub-vitreous, Crystal structure: Hexagonal (Microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6 - 2.9
Formation & geological history
Formed from silica-rich fluids depositing in sedimentary or volcanic environments. The black color usually results from organic impurities (bitumen) or iron sulfides trapped within the microcrystalline quartz structure.
Uses & applications
Primarily used for lapidary work, jewelry (beads and cabochons), metaphysical practice, and as a 'touchstone' for testing the purity of gold.
Geological facts
Black Jasper, specifically known as 'Basanite' when used for testing gold, has been used since ancient times. It remains functionally useful because when gold is rubbed on its surface, the streak's reaction to acid can determine the gold's karat value.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, waxy luster when tumbled. It is commonly found in riverbeds and coastal regions of the US (Oregon, California), Russia, and India.
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