metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, white, or light pink due to iron oxides; Luster: Vitreous to dull; Structure: Granular, non-foliated crystalline; Cleavage: None (fractures across grains).
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, white, or light pink due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, white, or light pink due to iron oxides; Luster: Vitreous to dull; Structure: Granular, non-foliated crystalline; Cleavage: None (fractures across grains).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the quartz grains, locking them into a dense, hard framework. Most specimens range from several hundred million to over a billion years old.
Uses & applications
Commonly used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silicon for glass making and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as prominent ridges or 'monadnocks' in the landscape. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than along the boundaries between them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. It is frequently found in mountain belts and Precambrian shields worldwide. Best found in glacial till or riverbeds in metabolic regions.
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