metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, can be reddish from iron; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan, can be reddish from iron
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, can be reddish from iron; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically in convergent plate boundaries. The original quartz grains recrystallize into a dense, interlocking mosaic of crystals.
Uses & applications
Used in construction as crushed stone or dimension stone, in manufacturing as a source of silica, and as decorative stone in landscaping or lapidary arts.
Geological facts
Quartzite is so tough that it often outlasts the mountains it forms, remaining as ridges or peaks while softer rocks erode away. It is often confused with marble but can be distinguished because quartzite will scratch glass and marble will not.
Field identification & locations
Identify in the field by its hardness (will scratch a steel knife) and its grainy, crystalline texture that breaks across grain boundaries rather than around them. Common in mountain ranges worldwide.
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