metamorphic
Quartzite
Metamorphic Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale. Color: Generally white, gray, or yellowish-brown, often showing speckled mineral grains. Luster: Vitreous to greasy on fresh surfaces. Crystal structure: Non-foliated, interlocking quartz grains. Cleavage: None (fractures across grains rather than along grain boundaries).…
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to greasy on fresh surfaces
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Physical properties
Hardness: 7 on the Mohs scale. Color: Generally white, gray, or yellowish-brown, often showing speckled mineral grains. Luster: Vitreous to greasy on fresh surfaces. Crystal structure: Non-foliated, interlocking quartz grains. Cleavage: None (fractures across grains rather than along grain boundaries). Specific gravity: 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under high tectonic heat and pressure. The original quartz grains recrystallize and weld tightly together, creating a rock much harder and more durable than the parent sandstone. Commonly found in mountainous regions and glaciated riverbeds.
Uses & applications
Used in construction, as crushed stone for road bases, railroad ballast, manufacturing silica bricks, and occasionally as decorative stone or for landscaping.
Geological facts
Quartzite is extremely resistant to weathering and chemical erosion, which is why quartz-rich pebbles and boulders frequently outlast other rock types in riverbeds and glacial deposits. Given the regional coordinate hint (northeastern Pennsylvania area), quartzite and quartz-bearing pebbles are very common due to local Appalachian folding and glacial drift.
Field identification & locations
Can be identified by testing hardness (will easily scratch glass and cannot be scratched by a steel knife) and checking for the absence of visible foliation layers. Often found smoothly rounded in stream beds and beaches due to high durability.
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