metamorphic
Quartzite (River Pebble)
Metamorphosed sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: yellowish-white to translucent cream; Luster: vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- yellowish-white to translucent cream
- Luster
- vitreous to waxy when polished
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Physical properties
Hardness: 7 on Mohs scale; Color: yellowish-white to translucent cream; Luster: vitreous to waxy when polished; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure, causing the sand grains to recrystallize and fuse together. This specific specimen has been further shaped by river or beach water erosion into a smooth, rounded pebble over thousands of years.
Uses & applications
Used as decorative landscaping stones, aquarium gravel, crushed stone in road construction, and occasionally in glassmaking or as a semi-precious stone for tumbling and jewelry if highly translucent.
Geological facts
Quartzite is often harder than the sandstone from which it originated. It is so tough that it usually breaks through the quartz grains rather than along the boundaries between them. It is one of the most resistant rocks to chemical weathering.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel) and its granular, sugary appearance inside. Commonly found in riverbeds, mountain gravel deposits, and glacial tills where harder minerals have survived transport.
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