metamorphic
Quartzite (Iron-Stained)
Quartzite (SiO2 with Fe2O3 inclusions)
Hardness: 7 (Mohs scale); Color: Orange, reddish-brown, tan, and gray due to iron oxide staining; Luster: Vitreous to waxy; Structure: Crystalline/Granular; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Orange, reddish-brown, tan, and gray due to iron oxide staining; Luster: Vitreous to waxy; Structure: Crystalline/Granular; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in orogenic belts. The orange color is caused by the infiltration of iron oxides (hematite or limonite) into the pore spaces or grain boundaries during or after formation.
Uses & applications
Used as decorative stone, in construction as crushed stone or flux, and occasionally in lapidary for tumbling and cabochons. High-purity quartzite is also used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the caps of ridges and mountains. It is harder than steel and can easily scratch glass.
Field identification & locations
Identify by its sugary, granular texture and extreme hardness. It won't react with acid (unlike marble) and will scratch a steel knife blade. Commonly found in riverbeds or glacial tills as rounded cobbles.
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