sedimentary
Chert (specifically Flint or Jasperoid)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Grey, white, tan, and rusty iron-stained orange; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grey, white, tan, and rusty iron-stained orange
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grey, white, tan, and rusty iron-stained orange; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic debris (like sponge spicules or radiolarians) or by the replacement of carbonate minerals in limestone or dolostone. This specimen shows significant weathering and iron oxide staining from environmental exposure.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today it is used in road surfacing, as grinding media in ball mills, and occasionally in jewelry as lapidary material.
Geological facts
Chert is so hard it can scratch steel and was famously used in 'flintlock' firearms because it produces sparks when struck against iron or steel. The orange-brown staining on this piece is known as a 'desert varnish' or iron oxide patina.
Field identification & locations
Identify in the field by its extreme hardness, smooth waxy texture when broken, and curved (shell-like) fracture patterns. It is frequently found as nodules within limestone outcrops or as smooth river pebbles.
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