metamorphic
Red Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 (Mohs scale), Color: dark pinkish-red to brownish-red, Luster: vitreous to dull, Crystal structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 (Mohs scale), Color: dark pinkish-red to brownish-red, Luster: vitreous to dull, Crystal structure: trigonal (microcrystalline), Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the quartz grains to recrystallize and fuse together. These specimens are often found as water-worn cobbles in glacial till or riverbeds.
Uses & applications
Commonly used as decorative landscaping stone, crushed stone for road construction, and occasionally in architecture or as a collector's specimen for its rich color.
Geological facts
Quartzite is one of the hardest and most durable rocks found in the Earth's crust. The red color is typically caused by minute inclusions of iron oxides like hematite between the quartz grains.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass) and its grainy, sandpaper-like texture that sparkles slightly in light. It is common in regions with ancient mountain ranges or glacial deposits, such as the Upper Midwest of the USA.
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