metamorphic
Quartzite with Gneissic Banding
Quartzite (primarily SiO2) with mafic mineral inclusions
Hardness: 7 on Mohs scale; Color: Gray, white, and brown with dark bands; Luster: Vitreous to dull; Crystal structure: Non-foliated to weakly foliated crystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, and brown with dark bands
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, and brown with dark bands; Luster: Vitreous to dull; Crystal structure: Non-foliated to weakly foliated crystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, likely during an orogenic (mountain-building) event. The banding suggests a high-grade metamorphic environment involving recrystallization of impurities.
Uses & applications
Used primarily as aggregate in construction, road ballast, or as decorative landscaping stones. Higher quality varieties are used for countertops or floor tiles.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains. It is significantly more durable than the sandstone from which it originated.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sugary, crystalline texture. It is commonly found in metamorphic terranes and as water-worn cobbles in riverbeds or beaches.
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