metamorphic
Quartzite (Potentially Ferruginous)
Quartzite (SiO2)
Hardness: 7 on the Mohs scale (scratches glass). Color: Tan, beige, or light brown due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal microcrystals. Cleavage: None (conchoidal fracture). Specific Gravity: 2.63 - 2.65.
- Hardness
- 7 on the Mohs scale (scratches glass)
- Color
- Tan, beige, or light brown due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale (scratches glass). Color: Tan, beige, or light brown due to iron oxide staining. Luster: Vitreous to dull. Crystal structure: Trigonal/Hexagonal microcrystals. Cleavage: None (conchoidal fracture). Specific Gravity: 2.63 - 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause original quartz grains to recrystallize and fuse together. This specimen appears water-worn, suggesting secondary transport via river or glacial activity.
Uses & applications
Used primarily as crushed stone for road construction and railway ballast. High-quality quartzite is used for kitchen countertops and flooring. In industry, it is a source of silica for glass and silicon metal production.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming prominent ridges. It is frequently mistaken for marble, but unlike marble, it will not react (fizz) with acid.
Field identification & locations
Identify in the field by its extreme hardness and grainy, 'sugary' texture on fresh breaks. It is commonly found in ancient mountain belts and glacial till. Collectors look for unique colors or rounding in riverbeds.
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