metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored yellow, orange, or red by iron oxides; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored yellow, orange, or red by iron oxides; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events. The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative building stone for countertops and walls, and in some industrial glass-making processes if high purity.
Geological facts
Quartzite is so tough that it often outlasts many other rocks in weathering, frequently forming the caps of ridges and mountains. It is harder than steel and cannot be scratched by a knife blade.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its crystalline appearance which looks like sugared texture. Commonly found in old mountain ranges or as water-worn pebbles in riverbeds.
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