metamorphic
Quartzite
Quartzite (Primary mineral: Quartz, SiO2)
Hardness: 7 on the Mohs scale. Color: Typically white to gray, but can be pink or red due to iron oxide. Luster: Vitreous to waxy. Crystal structure: Hexagonal (though usually appears as a sugary, granular mass). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on the Mohs scale. Color: Typically white to gray, but can be pink or red due to iron oxide. Luster: Vitreous to waxy. Crystal structure: Hexagonal (though usually appears as a sugary, granular mass). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together with a silica cement. It is found in mountain belts globally, with formations ranging from the Proterozoic to the Paleozoic era.
Uses & applications
Used extensively in construction as road ballast, roofing granules, and as a decorative building stone. It is also used as dimension stone for countertops (often marketed as 'granite') and in the manufacture of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges and resistant mountain peaks. Unlike sandstone, which breaks around its grains, quartzite breaks across its grains due to the intense fusion during metamorphism.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to acid (unlike marble). It has a sugary or grainy appearance on fresh surfaces. Common locations include the Appalachian Mountains (USA), the Alps, and various locations in Brazil and South Africa.
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