metamorphic
Quartzite (or Massive Quartz)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: White to tan with orange-brown iron staining; Luster: Vitreous to greasy; Crystal Structure: Trigonal (often appearing massive or crushed internally); Fracture: Conchoidal to irregular
- Hardness
- 7 (Mohs scale)
- Color
- White to tan with orange-brown iron staining
- Luster
- Vitreous to greasy
Identified More metamorphic →
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Physical properties
Hardness: 7 (Mohs scale); Color: White to tan with orange-brown iron staining; Luster: Vitreous to greasy; Crystal Structure: Trigonal (often appearing massive or crushed internally); Fracture: Conchoidal to irregular
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone or through hydrothermal vein cooling. Found in France, specifically the Massif Central region nearby Montgesty, which features various ancient metamorphic and crystalline basement rocks.
Uses & applications
Used in construction as crushed stone, road ballast, and occasionally as a flux in metallurgy or for landscaping.
Geological facts
Massive quartz and quartzite are resistant to chemical weathering, leading them to often appear as prominent outcrops or durable cobbles in riverbeds. The orange staining is typically due to limonite or iron oxide infiltration into micro-fractures.
Field identification & locations
Identify by its ability to scratch glass and steel, non-reactivity to acid, and lack of cleavage. In Montgesty, these can be found in alluvial deposits or as erosion remnants from nearby upland plateaus.
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