sedimentary
Ferruginous Chert
Silicon dioxide with iron oxide impurities (SiO2 + Fe2O3)
Hardness: 7 (Mohs scale); Color: Dark reddish-brown to maroon; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Dark reddish-brown to maroon
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Dark reddish-brown to maroon; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the chemical precipitation of silica-rich fluids in sedimentary environments. The dark red color is due to the presence of hematite or other iron oxides during formation.
Uses & applications
Used historically for stone tools due to its conchoidal fracture; modernly used as decorative landscaping rock or for lapidary work like cabochons.
Geological facts
Commonly associated with Banded Iron Formations (BIFs) which date back over 2 billion years; it is a primary source for understanding early Earth atmospheric conditions.
Field identification & locations
Identify by its hardness (it will scratch glass), its smooth, shell-like fracture surfaces, and its high density compared to some other sedimentary rocks. Commonly found in creek beds or glacial till near banded iron deposits.
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