metamorphic
Quartzite
Metamorphic rock consisting largely of Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: White, grayish, or brownish; Luster: Vitreous to dull; Crystal structure: Granular, interlocking quartz grains; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- White, grayish, or brownish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grayish, or brownish; Luster: Vitreous to dull; Crystal structure: Granular, interlocking quartz grains; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. The location in Southern Brazil (Rio Grande do Sul region) is consistent with the presence of recycled sediments and metamorphic basement rocks common in the Gondwana sequences.
Uses & applications
Used primarily in construction as crushed stone for road grit or railway ballast, as building facades, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along their boundaries, unlike its parent sandstone. It is extremely resistant to chemical weathering.
Field identification & locations
Identify by its ability to scratch glass (hardness 7) and its sugary/granular texture. It is often found in mountainous regions or as resistant outcrops in riverbeds. Common in the Brazilian Shield areas.
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