metamorphic
Quartzite Pebble
Metamorphic Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Off-white to grayish with dark gray/blackish veins. Luster: Dull to waxy/vitreous when worn. Crystal Structure: Trigonal (microcrystalline/interlocking). Cleavage: None (conchoidal to uneven fracture). Specific Gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Color
- Off-white to grayish with dark gray/blackish veins
- Luster
- Dull to waxy/vitreous when worn
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Physical properties
Hardness: 7 on Mohs scale. Color: Off-white to grayish with dark gray/blackish veins. Luster: Dull to waxy/vitreous when worn. Crystal Structure: Trigonal (microcrystalline/interlocking). Cleavage: None (conchoidal to uneven fracture). Specific Gravity: ~2.65.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing quartz grains to recrystallize and interlock tightly. Water erosion smoothed this specimen into a river pebble.
Uses & applications
Landscaping, aggregate in construction, and lapidary tumbling for amateur collectors.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering. When struck, quartzite breaks across its quartz grains rather than along their boundaries, unlike original sandstone.
Field identification & locations
Identified by its hardness (scratches glass easily), lack of cleavage, milky to grayish body, and rounded stream-worn texture. Commonly found in riverbeds, glacial deposits, and gravel bars worldwide.
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