metamorphic
Quartzite (Ferruginous)
Metamorphosed Quartz Sandstone (SiO2 with Iron oxide staining)
Hardness: 7 (Mohs scale), Color: Brownish-yellow to tan due to iron staining, Luster: Vitreous to greasy, Structure: Granular/Massive, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-yellow to tan due to iron staining, Luster: Vitreous to greasy, Structure: Granular/Massive, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed via the metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization of sand grains into a tight interlocking network. The brownish-yellow hue is caused by secondary infiltration of iron oxides like limonite or goethite.
Uses & applications
Used as a decorative stone in landscaping, as aggregate in road construction due to its extreme hardness, and occasionally for primitive tools in prehistory. Collector value is primarily for geological interest.
Geological facts
Quartzite is so hard and dense that when struck, it will break through the quartz grains themselves rather than around them, unlike its precursor sandstone. Iron-stained versions are often mistaken for jasper or citrine.
Field identification & locations
Identify in the field by its inability to be scratched by steel and its granular, crystalline texture. It is extremely resistant to weathering and is often found as resistant ridges or rounded river cobbles.
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