metamorphic
Quartzite with Mica
Metamorphic Quartzite (SiO2 + Mica phyllosilicates)
Hardness: 7 (Quartz) to 2.5 (Mica), Color: Grey, white, and silver, Luster: Vitreous to pearly, Crystal structure: Hexagonal/trigonal (quartz) and monoclinic (mica), Cleavage: None (quartz) to perfect basal (mica)
- Hardness
- 7 (Quartz) to 2
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Physical properties
Hardness: 7 (Quartz) to 2.5 (Mica), Color: Grey, white, and silver, Luster: Vitreous to pearly, Crystal structure: Hexagonal/trigonal (quartz) and monoclinic (mica), Cleavage: None (quartz) to perfect basal (mica)
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, often during mountain-building events (orogeny). Contains mica flakes formed by the alteration of clay minerals.
Uses & applications
Used in construction as crushed stone, floor tiles, and decorative stone. Sometimes used in glass making if pure enough. High-mica versions are primarily collector specimens.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them. It is one of the most chemically and physically resistant rocks on Earth's surface.
Field identification & locations
Identified by its sugary texture and the way it scratches glass. Found in mountainous or shield regions like the Appalachians or the Canadian Shield. Field identification relies on hardness and the lack of effervescence with acid.
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