metamorphic
Red Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: Reddish-orange due to iron oxide inclusions, Luster: Vitreous when wet or polished, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.8
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Physical properties
Hardness: 7 (Mohs scale), Color: Reddish-orange due to iron oxide inclusions, Luster: Vitreous when wet or polished, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.8
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic plate collisions and mountain-building events. The red hue comes from hematite or iron oxide staining within the quartz grains.
Uses & applications
Used as decorative stone in landscaping, aquarium accents, lapidary workshops for tumbling, and industrially as crushed stone for road construction and railway ballast.
Geological facts
Quartzite is so durable that it often remains as resistant ridges or outcrops while surrounding softer rocks erode away. It is harder than the steel of a knife, which helps distinguish it from similar-looking calcite or marble.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through grains rather than around them. Common in riverbeds and glacial deposits. Collectors value smoothly water-worn specimens.
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