metamorphic
Quartzite (River Siltstone variety)
Quartzite (SiO2)
Hardness: 7 Mohs; Color: Pale greenish-grey to off-white; Luster: Vitreous to waxy (when polished); Crystal Structure: Non-foliated, granular; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 Mohs
- Color
- Pale greenish-grey to off-white
- Luster
- Vitreous to waxy (when polished)
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Physical properties
Hardness: 7 Mohs; Color: Pale greenish-grey to off-white; Luster: Vitreous to waxy (when polished); Crystal Structure: Non-foliated, granular; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone or siltstone under intense heat and pressure, typically during tectonic plate collisions. This specific specimen has been further smoothed by fluvial (river) erosion over thousands of years.
Uses & applications
Used as decorative landscaping stones, aquarium substrate, or aggregate in construction. High-purity quartzite is used in the glass and metallurgy industries.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains because it resists weathering better than surrounding rocks.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and its sugary, crystalline texture under a magnifying lens. It is commonly found in riverbeds, glacial deposits, and mountain ranges globally.
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