metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often showing pink, red, or brown due to iron impurities; Luster: Vitreous to dull; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None, fractures conchoidally; 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 showing pink, red, or brown due to iron impurities; Luster: Vitreous to dull; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None, fractures conchoidally; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original sand grains recrystallize into an interlocking mosaic.
Uses & applications
Used as a decorative stone in construction (countertops, floor tiles), as railway ballast, and in the production of glass and silicon due to high silica content.
Geological facts
Quartzite is so tough that it often outlasts neighboring rocks during erosion, forming the peaks of many mountain ranges. It is frequently mistaken for marble but is much harder and will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its grainy, sandpaper-like texture that lacks the fizzing reaction to HCl. Found worldwide in ancient mountain belts.
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