metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 (Mohs scale), Color: off-white to tan/grey, Luster: Vitreous to dull when weathered, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal or irregular fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: off-white to tan/grey, Luster: Vitreous to dull when weathered, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal or irregular fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events (orogeny) in continental plates. Frequently found in Precambrian and Paleozoic formations.
Uses & applications
Commonly used as a decorative stone in landscaping, a raw material for glass making (if pure high-silica), railway ballast, road construction, and occasionally for primitive stone tools due to its hardness.
Geological facts
Unlike sandstone, which breaks around individual sand grains, quartzite is so well-fused that it breaks through the sand grains themselves. It is one of the most chemically and mechanically resistant rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and stainless steel) and its crystalline, sugary appearance on fresh breaks. It won't effervesce with acid, distinguishing it from marble. Common in mountain ranges and glacial deposits.
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