metamorphic
Quartzite (Iron-stained)
Quartzite (mostly SiO2 with Fe2O3 impurities)
Hardness: 7 on Mohs scale; Color: Pinkish-orange to white; Luster: Vitreous to waxy; Structure: Granular/Crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-orange to white
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-orange to white; Luster: Vitreous to waxy; Structure: Granular/Crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together, creating an extremely durable rock. The orange hue is likely due to iron oxide staining during or after formation.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glass making and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of hills and ridges. It is frequently mistaken for marble, but unlike marble, it will not fizz in contact with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its grainy, sugary texture. This specimen appears water-worn or weathered into a smooth pebble shape, commonly found in desert washes or riverbeds.
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