metamorphic
Quartzite (or Ferruginous Quartzite)
Metamorphosed Quartz Sandstone (SiO2 with Fe2O3 impurities)
Hardness: 7 (Mohs scale); Color: Brown, reddish-tan, or buff due to iron oxide staining; Luster: Dull to vitreous; Structure: Granular, non-foliated; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Brown, reddish-tan, or buff due to iron oxide staining
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: Brown, reddish-tan, or buff due to iron oxide staining; Luster: Dull to vitreous; Structure: Granular, non-foliated; Cleavage: None (conchoidal fracture); SG: 2.6-2.7.
Formation & geological history
Formed through the metamorphism (high heat and pressure) of quartz-rich sandstone. The reddish/brownish tint comes from iron minerals like hematite or goethite leaching into the porous parent sandstone before or during metamorphism. It can be found in mountain belts and areas of ancient shield rock worldwide.
Uses & applications
Used primarily in heavy construction, road ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica for glassmaking and metallurgy.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of hills and ridges because it resists weather much better than surrounding rocks. It can also be harder than a steel knife, which is a key identification test.
Field identification & locations
Identify in the field by its inability to be scratched by steel and its grainy, 'sugar-like' appearance on fresh breaks. This specific specimen is likely a water-worn river pebble, evidenced by its rounded, smooth shape created by fluvial erosion.
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