metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white to yellowish-tan due to iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (internal micro-crystals); Cleavage: none (conchoidal fracture); Specific gravity: 2.63-2.65
- Hardness
- 7 on Mohs scale
- Color
- white to yellowish-tan due to iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white to yellowish-tan due to iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (internal micro-crystals); Cleavage: none (conchoidal fracture); Specific gravity: 2.63-2.65
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing individual quartz grains to recrystallize and fuse together. Often found in orogenic belts.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative building stone, in the manufacture of glass and ceramics, and as a durable material for countertops.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, which distinguishes it from sandstone. Many mountain ranges, like the Appalachian Mountains, contain large quartzite ridges because it is highly resistant to weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary texture. Common in riverbeds and mountainous terrain. Collectors should look for smoothness from water erosion.
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