sedimentary
Jasper (Iron-stained Chert)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Dark grey/blue-grey with orange-brown iron staining and crackle patterns. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Dark grey/blue-grey with orange-brown iron staining and crackle patterns. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz crystals). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids in ocean environments, often undergoing metamorphic-like pressure during burial. The 'crackle' texture suggests weathering and mineralization of micro-fractures over millions of years.
Uses & applications
Used primarily in lapidary work for cabochons, beads, and pocket stones. It is also a popular specimen for rock tumbling and as an ornamental garden stone.
Geological facts
This specimen appears to be a stream-rolled or ocean-tumbled nodule. Jasper is an opaque form of chalcedony, and its name comes from the Greek 'iaspis', meaning 'spotted stone'.
Field identification & locations
Identify in the field by its high hardness (it will scratch glass), smooth waxy texture when wet, and lack of visible grains. Commonly found in riverbeds and coastal gravels where silica-rich deposits have eroded.
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