metamorphic
Quartzite
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or tan; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, can be yellow or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can be yellow or tan; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse into a dense, interlocking matrix. Usually associated with orogenic (mountain-building) belts.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. Highly sculptural pieces are used in landscaping or as decorative garden rocks.
Geological facts
Quartzite is so hard that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone which breaks around the grains.
Field identification & locations
Identify in the field by its extreme hardness (will scratch glass and steel) and its granular, sugary appearance. Found globally in ancient mountain ranges and as water-worn pebbles in riverbeds.
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