metamorphic
Quartzite (Ferruginous)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Reddish-brown to pink (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Granular, interlocking quartz grains; Specific Gravity: 2.6 to 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Reddish-brown to pink (due to iron oxide)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Reddish-brown to pink (due to iron oxide); Luster: Vitreous to dull; Crystal structure: Granular, interlocking quartz grains; Specific Gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic activity cause individual quartz grains to recrystallize and fuse together, typically occurring during mountain-building events.
Uses & applications
Used as a decorative stone in landscaping and flooring, as railway ballast, and in the production of glass or silicon ceramics when pure. Small specimens are popular in educational rock kits.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it forms, leading to the creation of resistant ridges and peaks. It is significantly harder and more durable than the parent sandstone.
Field identification & locations
Identify in the field by its inability to be scratched by a steel nail and its tendency to break across quartz grains rather than around them (unlike sandstone). Found globally in ancient tectonic belts and mountain ranges.
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