metamorphic
Quartzite with Iron Staining
Quartzite (primarily SiO2 with Fe2O3 staining)
Hardness: 7 on Mohs scale; Color: Orange-brown surface due to iron oxides, white/gray interior; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Orange-brown surface due to iron oxides, white/gray interior
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Orange-brown surface due to iron oxides, white/gray interior; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The orange color is a secondary 'desert varnish' or iron oxidation from weathering.
Uses & applications
Used primarily in construction as crushed stone or road ballast; higher quality specimens are used for decorative landscaping, floor tiles, and occasionally lapidary work.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the peaks of hills and ridges. It is harder and more durable than its parent rock, sandstone.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its grainy, sugary texture. Unlike sandstone, it breaks through the quartz grains rather than around them. Found globally in ancient mountain belts.
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