metamorphic
Ferruginous Quartz (Iron-stained Quartzite)
Silicon Dioxide (SiO2) with Hematite/Limonite impurities
Hardness: 7 (Mohs scale), Color: Tan to reddish-orange with white interiors, Luster: Vitreous to dull (if weathered), Crystal Structure: Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Tan to reddish-orange with white interiors, Luster: Vitreous to dull (if weathered), Crystal Structure: Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize. The orange/red staining occurs as iron-rich groundwater percolates through cracks in the rock over geological time.
Uses & applications
Commonly used in construction as aggregate or road base. Rounded specimens like this are often used in landscaping or rock tumbling. Some high-purity varieties are used in glass manufacturing.
Geological facts
Quartz is the most abundant mineral in the Earth's continental crust. These water-worn river rocks can travel hundreds of miles from their original source, becoming smoothed and rounded through abrasion.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its lack of reaction to acid. Look for the granular, 'sugar-like' texture typical of quartzite combined with orange staining on the outer rind.
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