metamorphic
Quartzite (Ferruginous)
SiO2 (Metamorphosed Sandstone)
Hardness: 7 on Mohs scale; Color: Reddish-purple to grey with banded patterns; Luster: Vitreous to dull when weathered; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Reddish-purple to grey with banded patterns
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-purple to grey with banded patterns; Luster: Vitreous to dull when weathered; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. The reddish tint suggests the presence of iron oxide (hematite) during formation.
Uses & applications
Large-scale deposits are used for crushed stone in construction, road ballast, and as a source of silica for glass manufacturing. Polished pebbles are used for decorative landscaping and lapidary hobbies.
Geological facts
Quartzite is so strong that it usually breaks through the quartz grains rather than around their boundaries, unlike the sandstone from which it originated. It is often more resistant to weathering than the surrounding rock.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass and steel) and its grainy, sandpaper-like texture that doesn't rub off. Often found as rounded river or beach cobbles. Commonly located in mountainous regions with ancient tectonic activity.
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