metamorphic
Quartz-rich metamorphic rock, likely quartzite
Quartzite; predominantly crystalline SiO₂, with possible mica, feldspar, and iron-oxide impurities
AI-generated identification · may be incorrectTypically Mohs hardness 7, gray to brown with a granular texture and vitreous to dull luster. Interlocking quartz grains show no obvious cleavage; the dark streaks and greenish patches may reflect mica, chlorite, or weathering minerals.
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Physical properties
Typically Mohs hardness 7, gray to brown with a granular texture and vitreous to dull luster. Interlocking quartz grains show no obvious cleavage; the dark streaks and greenish patches may reflect mica, chlorite, or weathering minerals.
Formation & geological history
Formed when quartz-rich sandstone recrystallizes under intense heat and pressure during regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined from the photograph and depends on locality.
Uses & applications
Used as crushed stone, aggregate, road material, and durable building or paving stone; attractive pieces may be sold as landscaping or cabinet specimens. It has limited jewelry use unless exceptionally colorful or patterned.
Geological facts
Quartzite commonly fractures across grains rather than around them, unlike sandstone, and can be harder than a steel knife. The specimen may alternatively be a quartz-rich metamorphic cobble such as metasandstone.
Field identification & locations
In the field, test a fresh surface with a steel file or glass: quartzite generally scratches glass and resists scratching by steel. Common occurrences include metamorphic mountain belts worldwide, especially India, Brazil, the United States, and Scandinavia.
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