Quartzite
Quartzite is a hard metamorphic rock formed by the recrystallization of quartz sandstone under heat and pressure, fusing individual quartz grains into an interlocking mosaic so tightly bonded that fractures cut through the grains themselves rather than around them. This distinguishes true metamorphic quartzite from sedimentary orthoquartzite, a well-cemented sandstone that can look superficially similar. Its exceptional hardness and resistance to weathering make it a common ridge-forming rock in many mountain ranges.
Quartzite properties at a glance
| Type | Metamorphic Rocks |
|---|---|
| Mohs hardness | 7 |
| Luster | Vitreous to sugary/granular |
| Fracture | Conchoidal |
| Specific gravity | 2.6–2.7 |
| Transparency | Opaque |
| Common colors | White, Gray, Pink, Reddish, Yellow |
| Rarity | common |
Geology & background
Quartzite forms through regional or, less commonly, contact metamorphism of quartz-rich sandstone, where recrystallization welds the original sand grains into a dense, interlocking quartz mosaic while largely erasing the original sedimentary texture, though relict bedding or cross-bedding sometimes survives in less intensely recrystallized examples. Because pure quartz sand is chemically simple, quartzite typically contains few minerals besides quartz itself, with occasional mica, iron oxide, or other minor accessories adding color variation. Notable quartzite ranges include the Baraboo Range in Wisconsin, South Africa's Witwatersrand quartzites, and India's Vindhyan quartzite ridges.
Rockhounds appreciate quartzite for its durability and often striking coloration, running from white and gray to pink, red, or purple depending on iron oxide or other trace impurities, which makes it popular for both scientific study and decorative building stone. Because it resists weathering so effectively, quartzite frequently forms prominent ridges and hills that stand higher than surrounding, more easily eroded rock. Collectors should learn to distinguish true metamorphic quartzite, which breaks through grains, from sedimentary orthoquartzite, which can fracture around grains along original cement boundaries.
How to identify Quartzite
Quartzite is typically white, gray, pink, or reddish, with a vitreous to slightly greasy luster and a white streak, and its hardness of about 7, equal to quartz itself, lets it easily scratch glass and resist a steel knife. It has no true cleavage and breaks with a conchoidal to splintery fracture that cuts directly through the interlocking quartz grains rather than around them. Grain boundaries are often hard to spot without a hand lens, giving the rock a sugary or glassy texture. It is most often confused with quartz-cemented sandstone or with marble, though quartzite scratches glass while marble does not.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Quartzite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Quartzite worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Field identification
- Metamorphic history study
- Decorative or building stone when suitable
- Education
Interesting facts
- True metamorphic quartzite is so tightly fused that a fracture will break straight through individual quartz grains rather than following the boundaries between them.
- Because it resists erosion so well, quartzite commonly forms the resistant caprock of ridges and hills long after surrounding softer rock has worn away.
- Ancient quartzite outcrops, some over a billion years old, preserve ripple marks and other sedimentary features from long-vanished beaches and riverbeds.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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