metamorphic
Quartzite River Cobble
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Light gray to tan/white; Luster: Dull to vitreous; Structure: Granular, non-foliated; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Light gray to tan/white
- Luster
- Dull to vitreous
Identified More metamorphic →
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Physical properties
Hardness: 7 (Mohs scale); Color: Light gray to tan/white; Luster: Dull to vitreous; Structure: Granular, non-foliated; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. This specimen shows significant rounding and smoothing due to fluvial (river) erosion over many years.
Uses & applications
Commonly used as decorative landscape stone, construction aggregate, and in railroad ballast. High-purity quartzite is used to produce glass and metallic silicon.
Geological facts
Quartzite is one of the most durable rocks on Earth's surface. When it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone.
Field identification & locations
Identified by its high hardness (it will scratch glass/steel) and sugary, granular texture. Commonly found in riverbeds, glacial deposits, and mountain ranges where ancient sandstone was buried.
