metamorphic
Quartzite
Metaquartzite (predominantly SiO2)
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale; vitreous to sugary luster on fresh breaks; dull to waxy when water-worn; reddish-purple to brownish-pink color (due to iron oxide/hematite inclusions); interlocking crystalline texture with conchoidal to uneven fracture; specific gravity approximately 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; vitreous to sugary luster on fresh breaks; dull to waxy when water-worn; reddish-purple to brownish-pink color (due to iron oxide/hematite inclusions); interlocking crystalline texture with conchoidal to uneven fracture; specific gravity approximately 2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone under intense heat and tectonic pressure. During recrystallization, quartz grains fuse together into a dense, non-foliated interlocking network. Common in Precambrian shields and fold-and-thrust mountain belts.
Uses & applications
Extensively used as crushed stone for railway ballast, highway construction, and riprap due to extreme hardness and durability; also used in decorative landscaping, dimension stone, and as a silica source in metallurgical processes.
Geological facts
Unlike sandstone, which breaks around individual sand grains leaving a sandpaper-like surface, quartzite fractures across the individual grains, producing a glassy or sparkling granular break. Many famous formations, such as the Sioux Quartzite or Baraboo Quartzite in North America, are over a billion years old.
Field identification & locations
Field identification relies on testing hardness (it easily scratches glass and stainless steel knives) and observing the fused quartz grains that sparkle slightly in bright light. Rounded river pebbles like this one are commonly found in glacial drift, riverbeds, and gravel deposits downstream of metamorphic terrains.
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