metamorphic
Ferruginous Quartzite (Chert)
Quartzite with Iron inclusions (SiO2 + Fe2O3)
Hardness: 7 on Mohs scale. Color: Reddish-brown, tan, orange-brown (due to iron oxidation). Luster: Dull to waxy. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown, tan, orange-brown (due to iron oxidation)
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: Reddish-brown, tan, orange-brown (due to iron oxidation). Luster: Dull to waxy. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone or the silification of sedimentary deposits. The reddish-brown color comes from iron oxides staining the quartz during or after formation. Most specimens date from the Proterozoic to Paleozoic eras.
Uses & applications
Used primarily in landscaping, road construction as aggregate, and occasionally by flint-knappers for making stone tools. It is also collected by hobbyists for tumbling.
Geological facts
Quartzite is so hard that it will scratch glass and steel. This specific iron-rich variety is often mistaken for petrified wood or common jasper because of its earthy color palette.
Field identification & locations
Identify in the field by its extreme hardness, lack of horizontal grain (unlike sandstone), and its rough, grainy surface texture that still shows a spark when struck with steel. Commonly found in riverbeds and glacial till.
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