metamorphic
Quartzite Pebble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and reddish-brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish-brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. This specific specimen is a water-worn river pebble, having been rounded by fluvial erosion over thousands of years.
Uses & applications
Used as a decorative landscape stone, in road construction, and as a source of silica in glass manufacturing. Smooth pebbles are often used in aromatherapy and massage.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is one of the most durable and resistant rocks on Earth's surface, which is why it often survives as a pebble long after other rocks have eroded away.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and its sugary, crystalline texture when broken. It lacks the internal banding of agate and is much harder than limestone. Common in river beds and glacial till.
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