metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish; Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pinkish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish; Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization of quartz grains. Geological ages vary widely from Precambrian to Cenozoic.
Uses & applications
Used as crushed stone in road construction, railroad ballast, and as decorative stone in countertops, tiles, and landscaping. Highly valued for its durability and resistance to weathering.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. It is often confused with marble but is significantly harder.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it fractures through the quartz grains rather than around them. Common in folded mountain belts.
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