sedimentary
Chert (Iron-stained)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to yellowish-brown (due to iron oxide staining); Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan to yellowish-brown (due to iron oxide staining)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to yellowish-brown (due to iron oxide staining); Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a specimen for amateur geology collections.
Geological facts
Chert is so hard it can strike sparks against steel. The brownish color of this specific piece is caused by secondary weathering and the inclusion of Limonite or Goethite.
Field identification & locations
Identify by its hardness (will scratch glass) and smooth, shell-like fracture surfaces. Commonly found in limestone or dolomite beds as nodules or layers.
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