metamorphic
Ferruginous Quartzite (Iron-stained Quartz)
Quartzite (SiO2 with Fe-oxide staining)
Hardness 7 (Mohs scale), colors ranging from brownish-grey to rusty orange/yellow due to iron oxides, vitreous to dull luster, granular texture, lacks cleavage, specific gravity ~2.65.
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Physical properties
Hardness 7 (Mohs scale), colors ranging from brownish-grey to rusty orange/yellow due to iron oxides, vitreous to dull luster, granular texture, lacks cleavage, specific gravity ~2.65.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. The iron staining occurs through secondary weathering or hydrothermal fluids containing iron minerals like limonite or hematite.
Uses & applications
Used primarily as construction aggregate, railway ballast, and decorative garden landscaping stone. High-purity quartzite can be used to produce glass or silicon.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them. It is one of the most chemically resistant rocks on the Earth's surface.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for granular texture reminiscent of sand but fused into a solid mass. Commonly found in mountainous regions or ancient cratons.
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