metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale. Color: white to grey, with pink or reddish tints from iron oxides. Luster: vitreous to dull. Texture: granular and crystalline. Cleavage: none (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on the Mohs scale
- Color
- white to grey, with pink or reddish tints from iron oxides
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: white to grey, with pink or reddish tints from iron oxides. Luster: vitreous to dull. Texture: granular and crystalline. Cleavage: none (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, erasing the original sedimentary texture. This process typically occurs in mountain-building regions.
Uses & applications
Used as crushed stone for road construction and railway ballast. Due to its hardness and resistance to weathering, it is used for building stone, floor tiles, and kitchen countertops. In manufacturing, it is a source of silica for glass and ceramics.
Geological facts
Quartzite is so tough that it usually breaks across the quartz grains rather than along the boundaries between them, which distinguishes it from sandstone. Some varieties can be over 1 billion years old.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. It lacks the layering seen in schist or the visible individual sand grains found in sandstone. Common in mountain ranges and ancient shield areas.
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