metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale. Color: Gray, tan, or brown. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Gray, tan, or brown. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original quartz sand grains recrystallize and fuse together.
Uses & applications
Used in construction as crushed stone for road beds or railway ballast, as decorative stone in countertops and tiles, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is more resistant to weathering than most other rocks, often forming the caps of prominent ridges or hills.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular texture that looks like sandstone but breaks through the grains rather than around them. Found globally in ancient mountain belts.
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