metamorphic
Quartzite with Epidote
Meta-quartzite containing Epidote (Ca2(Al2,Fe)(SiO4)(Si2O7)O(OH))
Hardness: 6-7 on Mohs scale; Color: Off-white to gray with greenish streaks; Luster: Vitreous to dull; Structure: Granoblastic (metamorphosed sand grains); Cleavage: None/Conchoidal fracture.
- Hardness
- 6-7 on Mohs scale
- Color
- Off-white to gray with greenish streaks
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Off-white to gray with greenish streaks; Luster: Vitreous to dull; Structure: Granoblastic (metamorphosed sand grains); Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. The green coloration indicates the presence of epidote, often resulting from hydrothermal alteration or low-grade metamorphism (greenschist facies).
Uses & applications
Primarily used as crushed stone for road construction and railway ballast; aesthetically pleasing pieces are used as decorative garden stones or for lapidary tumbling.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them. The green epidote suggests this rock underwent specific pressure and temperature conditions typical of transformative tectonic boundaries.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel crystalline knife) and its sugary, crystalline texture; common in mountain ranges and ancient shield areas. The presence of green minerals in a hard, non-foliated rock is a key field indicator.
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