metamorphic
Ferruginous Quartzite (Red Quartzite)
Quartzite (primarily SiO2 with Fe2O3 inclusions)
Hardness: 7 Mohs scale. Color: Reddish-brown, tan, and gray. Luster: Vitreous to dull. Crystal structure: Granular, non-foliated. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 Mohs scale
- Color
- Reddish-brown, tan, and gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 Mohs scale. Color: Reddish-brown, tan, and gray. Luster: Vitreous to dull. Crystal structure: Granular, non-foliated. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The reddish hue is caused by the presence of iron oxide (hematite) during or after recrystallization. Often associated with Proterozoic or Paleozoic geological formations.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking. Rough specimens are popular for landscape decoration and rock tumbling.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the tops of ridges and hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness and grainy, sugary appearance on fresh breaks. It is commonly found in glacial till, riverbeds, and mountainous regions like the Appalachians or the Canadian Shield. Collectors look for smooth, water-worn river stones like this one.
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