metamorphic
Limonitic Quartzite
Metamorphosed sandstone with Limonite (FeO(OH)·nH2O) staining
Hardness: 7 (Mohs scale), Color: Grayish-white with yellow-orange iron staining, Luster: Vitreous to dull, Crystal structure: Granular/Massive, Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Grayish-white with yellow-orange iron staining, Luster: Vitreous to dull, Crystal structure: Granular/Massive, Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse. The yellow staining is from secondary iron oxide weathering (limonite).
Uses & applications
Used primarily as construction aggregate, railway ballast, and sometimes in decorative landscaping or as industrial silica source.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along their boundaries, unlike its parent rock sandstone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy but fused texture. Often found in Appalachian or mountainous regions.
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