metamorphic
Quartzite with Iron inclusions
Metamorphosed Sandstone (SiO2 with Fe2O3)
Hardness: 7 (Mohs scale), Color: tan to orange-brown (due to iron oxidation), Luster: earthy to vitreous on fresh breaks, Crystal structure: granular/crystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to orange-brown (due to iron oxidation), Luster: earthy to vitreous on fresh breaks, Crystal structure: granular/crystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the recrystallization of quartz-rich sandstone through intense heat and pressure (metamorphism). The orange-red staining is caused by secondary iron oxide (limonite or hematite) leaching into the rock's fractures and pores.
Uses & applications
Commonly used as crushed stone in construction, road ballast, and decorative landscaping. High-purity quartzite is used in glassmaking and as a source for silicon.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them. This specimen shows significant 'desert varnish' or iron staining, which is common in weathered surface exposures.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and its granular, sugary texture. It is often found in mountainous regions or stable shield areas where ancient seabeds were buried and uplifted.
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