metamorphic
Quartz-rich metamorphic pebble, likely quartzite
Quartzite; predominantly crystalline quartz (SiO₂), with possible feldspar and mica impurities
AI-generated identification · may be incorrectHardness about 7 Mohs; pale gray to tan, with a granular crystalline texture and vitreous to dull luster. Quartzite has no prominent cleavage, irregular fracture, and typically high durability; the image alone cannot confirm exact composition.
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Physical properties
Hardness about 7 Mohs; pale gray to tan, with a granular crystalline texture and vitreous to dull luster. Quartzite has no prominent cleavage, irregular fracture, and typically high durability; the image alone cannot confirm exact composition.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under intense heat and pressure during metamorphism, commonly during mountain-building events. Its age depends on the parent sandstone and metamorphic episode, often millions to billions of years.
Uses & applications
Used as crushed stone, aggregate, paving, slabs, and decorative stone; attractive pieces are collected but usually have modest gem value.
Geological facts
Quartzite is commonly confused with sandstone, but its quartz grains are fused together and it generally scratches glass. Iron staining can produce the tan or rusty coloration visible here.
Field identification & locations
Look for a sugary crystalline surface, very high hardness, and grains that break across rather than around the rock; acid produces no reaction. Common in metamorphic mountain belts worldwide, including Brazil, India, Scandinavia, and the United States.
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