metamorphic
Quartzite (Ferruginous)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Yellowish-tan to brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline clusters); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-tan to brown due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-tan to brown due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline clusters); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure during regional metamorphism. The original sand grains are recrystallized into an interlocking mosaic of quartz crystals. The yellow tint indicates the presence of iron impurities during or after formation.
Uses & applications
Used as a decorative stone, in construction as crushed stone for road beds, and as a raw material for glass manufacturing due to high silica content.
Geological facts
Quartzite is so durable that it can withstand millions of years of chemical and physical weathering, often forming the caps of prominent ridges and mountains.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its grainy, sandpaper-like surface that does not rub off. It is commonly found in riverbeds or near mountain ranges where tectonic plates have collided.
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