metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish tints from iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish tints from iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6-2.7.
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to high heat and pressure, typically during mountain-building events (orogeny). This causes the quartz grains to recrystallize and fuse together into a dense, hard rock. It can date back from the Precambrian to more recent eras.
Uses & applications
Extensively used in construction as crushed stone for road gravel and rail ballast. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. It is also used as decorative stone in landscaping and flooring.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming prominent ridges and hills. It is often confused with marble, but can be distinguished by its hardness; quartzite will scratch glass, while marble will not.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel blade) and its tendency to break across grain boundaries rather than around them (unlike sandstone). It is commonly found in metamorphic belts around the world, such as the Appalachian Mountains and the Scottish Highlands.
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