metamorphic
Quartzite (with Iron Oxide staining)
SiO2 (Quartzite / Weathered Sandstone)
Hardness: 7 on the Mohs scale. Color: Yellowish-brown to tan/orange due to limonite/hematite iron oxide staining, with sparkling white crystalline areas inside. Luster: Vitreous to dull. Cleavage: None (conchoidal to irregular fracture). Specific gravity: ~2.65.
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Yellowish-brown to tan/orange due to limonite/hematite iron oxide staining, with sparkling white crystalline areas inside. Luster: Vitreous to dull. Cleavage: None (conchoidal to irregular fracture). Specific gravity: ~2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, fusing the quartz grains together into a dense, hard crystalline rock. The yellowish coating is a secondary weathering effect caused by iron-rich water oxidation.
Uses & applications
Used extensively as a crushed stone in road construction, railroad ballast, decorative landscaping gravel, and high-durability building stone or countertops.
Geological facts
Unlike sandstone which fractures around constituent sand grains, quartzite is so strongly fused that it fractures directly through the quartz grains themselves, giving it a characteristic sugary sparkled fracture surface.
Field identification & locations
Identified by its extreme hardness (scratches glass easily), sugary crystalline texture that sparkles under direct sunlight, and distinct rusty iron oxide coating. Extremely common in ancient mountain belts, riverbeds, and glacial till.
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