metamorphic
River Rock (Quartzite)
Quartzite
Hardness: 7 on the Mohs scale. Color: Gray, brown, or tan. Luster: Vitreous to dull. Crystal structure: Granular/interlocking quartz crystals. Cleavage: None, breaks with a conchoidal fracture. Specific gravity: 2.65 to 2.75.
- Hardness
- 7 on the Mohs scale
- Color
- Gray, brown, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Gray, brown, or tan. Luster: Vitreous to dull. Crystal structure: Granular/interlocking quartz crystals. Cleavage: None, breaks with a conchoidal fracture. Specific gravity: 2.65 to 2.75.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure typically associated with tectonic compression during mountain building (orogeny). Age can range from Precambrian to Cenozoic depending on the specific location.
Uses & applications
Used in landscaping, construction, decorative pathways, and sometimes in architectural facings.
Geological facts
Quartzite is extremely durable and resistant to weathering, which is why rocks like this survive long journeys down rivers, becoming smooth and rounded.
Field identification & locations
Found worldwide in riverbeds, glacial tills, and mountainous regions. To identify in the field, check for high hardness (scratches glass) and lack of reaction to acid.
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