metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7, Color: white to light brown (often stained by iron), Luster: vitreous, Crystal structure: granoblastic, Cleavage: none, Specific gravity: 2.65
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Physical properties
Hardness: 7, Color: white to light brown (often stained by iron), Luster: vitreous, Crystal structure: granoblastic, Cleavage: none, Specific gravity: 2.65
Formation & geological history
Formed from the regional or contact metamorphism of quartz sandstone. The original quartz sand grains are fused together under high heat and pressure.
Uses & applications
Used in construction, as railway ballast, decorative stone, and sometimes as a raw material for silica.
Geological facts
Quartzite is so hard and dense that it usually breaks across the quartz grains rather than around them, unlike its parent rock, sandstone.
Field identification & locations
Identify by its hardness (scratches glass), sugary texture, and lack of fizzing with weak acid (unlike marble). Common in areas with ancient mountain building.
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