metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan, sometimes yellowish or brownish due to iron oxide; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (conchoidal fracture); 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: white, gray, or tan, sometimes yellowish or brownish due to iron oxide; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. High pressure and heat cause the individual quartz grains to recrystallize and fuse together into a dense, crystalline mass. It is found in mountain belts worldwide.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping or interior design. High-purity quartzite is used in the manufacturing of glass and silicon.
Geological facts
Quartzite is so hard that it will scratch glass. In some historical contexts, it was used to create stone tools because of its hardness and the way it fractures into sharp edges.
Field identification & locations
Identify in the field by its extreme hardness and way it breaks 'through' the sand grains rather than 'around' them like sandstone. It often has a slightly sugary appearance upon close inspection.
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