metamorphic
Quartzite (Nodule)
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull when weathered; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan
- Luster
- Vitreous to dull when weathered
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan; Luster: Vitreous to dull when weathered; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing sand grains to recrystallize into a dense, interlocking matrix. Usually associated with tectonic mountain-building events.
Uses & applications
Used primarily in construction for crushed stone, road ballast, and aggregate. Also utilized in making hearth bricks for furnaces and as decorative landscaping stones.
Geological facts
Quartzite is so hard that it will scratch glass and even high-quality steel tools. Unlike sandstone, which breaks around grains, quartzite breaks through the grains due to the complete fusion of quartz during metamorphosis.
Field identification & locations
Identify by its extreme hardness and lack of reaction to acid. Often found as rounded cobbles in stream beds or glacial till. Common in areas with ancient shield rocks or eroded mountain ranges.
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