metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: Light grey, whitish, to subtle greenish hues. Luster: Vitreous to sugary (saccharoidal). Texture: Granoblastic, interlocking quartz grains. Cleavage: None, breaks with a conchoidal or irregular fracture across quartz grains.
- Hardness
- 7 on the Mohs scale
- Color
- Light grey, whitish, to subtle greenish hues
- Luster
- Vitreous to sugary (saccharoidal)
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Physical properties
Hardness: 7 on the Mohs scale. Color: Light grey, whitish, to subtle greenish hues. Luster: Vitreous to sugary (saccharoidal). Texture: Granoblastic, interlocking quartz grains. Cleavage: None, breaks with a conchoidal or irregular fracture across quartz grains.
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone under intense heat and pressure, causing original quartz grains to recrystallize into a interlocking mosaic of quartz crystals.
Uses & applications
Used as crushed stone in construction, road base, railway ballast, decorative landscaping stone, dimension stone, and as a source of silica in glassmaking.
Geological facts
Unlike sandstone, which breaks around individual sand grains, quartzite is so strongly recrystallized that it breaks right through the quartz grains when fractured.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass easily) and sugary crystalline texture that fractures across grains rather than around them. Widely found in metamorphic rock terrains worldwide.
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