metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (harder than glass). Color: Grey, white, or yellowish-tan. Luster: Vitreous to dull. Structure: Granoblastic, non-foliated. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale (harder than glass)
- Color
- Grey, white, or yellowish-tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass). Color: Grey, white, or yellowish-tan. Luster: Vitreous to dull. Structure: Granoblastic, non-foliated. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartzose sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. Generally found in Precambrian to Paleozoic mountain belts.
Uses & applications
Used as crushed stone for road construction and railway ballast; also used as a decorative stone in architecture, countertops, and flooring due to its durability and resemblance to marble.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks; it frequently forms the caps of ridges and mountain peaks. Unlike sandstone, when broken, quartzite fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (it will easily scratch a knife blade or glass plate) and its sugary, crystalline texture. It is often found in riverbeds as rounded cobbles or on mountainous outcrops.
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