metamorphic
Limonite-stained Quartzite
Metamorphosed Quartz-rich Arenite (SiO2 with FeO(OH)·nH2O)
Hardness: 7 (Mohs scale); Color: Tan, yellow-brown to rusty orange; Luster: Dull to greasy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, yellow-brown to rusty orange
- Luster
- Dull to greasy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, yellow-brown to rusty orange; Luster: Dull to greasy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the regional metamorphism of quartz sandstone. The yellow-brown staining is due to limonite (iron oxide/hydroxide) weathering from nearby iron-rich minerals or groundwater infiltration.
Uses & applications
Used as a construction aggregate, rail ballast, and occasionally for decorative landscaping or historical toolmaking (flaked stone tools).
Geological facts
Quartzite is so tough that it often survives intense weathering and erosion better than the surrounding rocks, often forming the summits of hills or ridges. The yellow staining is a result of the 'rusting' of iron minerals.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and its granular, sugary texture. It is extremely common in areas with ancient mountain belts or glacial deposits.
