metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown (due to iron oxidation), Luster: vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown (due to iron oxidation), Luster: vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: none, Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny).
Uses & applications
Used as decorative stone in landscaping, crushed stone for road construction, and industrial silica source. Occasionally used for lapidary work if highly figured.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks as they wear away, forming prominent ridges and hills. It is often confused with marble but will scratch glass while marble will not.
Field identification & locations
Identify by its extreme hardness and grainy texture that breaks across grain boundaries rather than around them. Commonly found in metamorphic belts near convergent plate boundaries.
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