metamorphic
Quartzite River Rock
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (scratches glass); Color: light tan, white, or grey with iron-staining; Luster: dull to vitreous when wet; Crystal structure: Non-foliated, granular; Cleavage: none (fractures across grains).
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- light tan, white, or grey with iron-staining
- Luster
- dull to vitreous when wet
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Physical properties
Hardness: 7 on Mohs scale (scratches glass); Color: light tan, white, or grey with iron-staining; Luster: dull to vitreous when wet; Crystal structure: Non-foliated, granular; Cleavage: none (fractures across grains).
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. This specific specimen has been further shaped by fluvial erosion (river action), giving it its rounded 'cobble' appearance. Typical ages vary widely from Proterozoic to Cenozoic.
Uses & applications
Used primarily in construction as crushed stone or gravel, and frequently in landscaping for decorative riverbeds or paths. Higher purity quartzite is used to produce silicon metal or glass.
Geological facts
Quartzite is so durable that it often survives intense weathering that destroys other rocks. While it started as sandy beach deposits, the metamorphic process 'welds' the sand grains together so tightly that the rock will break through the grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, crystalline texture. Commonly found in riverbeds, glacial tills, and mountainous metamorphic belts. Collectors look for unique shapes or smooth textures.
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