metamorphic
Quartzite
Metamorphosed sandstone (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with green streaks from chlorite or epidote; Luster: vitreous to dull; Crystal Structure: non-foliated, granoblastic; Cleavage: none; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with green streaks from chlorite or epidote; Luster: vitreous to dull; Crystal Structure: non-foliated, granoblastic; Cleavage: none; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the individual quartz grains to recrystallize into a locked interlocking mosaic of crystals. This specimen appears water-worn, likely from a river or beach environment.
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. In crushed form, it's used for glass making and as an industrial abrasive. Polished pieces are used in jewelry and home decor.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming ridges and mountain peaks. Unlike sandstone, when quartzite breaks, it breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary appearance despite being a solid mass. Commonly found in folded mountain belts and ancient shield regions.
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