metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White to pale grey with green tints, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular), Cleavage: Indistinct/Conchoidal fracture, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to pale grey with green tints, Luster: Vitreous to dull, Crystal Structure: Trigonal (granular), Cleavage: Indistinct/Conchoidal fracture, Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the quartz grains, locking them into a tight network.
Uses & applications
Used in construction as road ballast, decorative stone in masonry, as a source for silica in metallurgy, and occasionally for lapidary work if it contains unique inclusions.
Geological facts
Quartzite is so hard that it can scratch glass and even steel. Its toughness makes it highly resistant to chemical weathering, which is why it often caps mountain peaks.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness. It won't react with acid (differentiating it from marble) and is much harder than limestone. Common in mountain ranges and ancient shield areas.
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