metamorphic
Quartzite (River Stone)
Quartzite (composed primarily of Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale), Color: White to grey with occasional darker mineral inclusions, Luster: Vitreous to dull (when weathered), Crystal Structure: Non-foliated/Granular, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to grey with occasional darker mineral inclusions, Luster: Vitreous to dull (when weathered), Crystal Structure: Non-foliated/Granular, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. The rounded shape indicates secondary weathering in a high-energy water environment, likely a river or coastal beach.
Uses & applications
Used widely in construction as road ballast and aggregate. In crushed form, it is used for sandblasting. High-purity quartzite is a source of silica for glassmaking. Smooth specimens are popular for home decor, landscaping, and lapidary tumbling.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than along the boundaries between them. It is one of the most durable rocks on Earth's surface and is often found as 'erratics' far from its source due to glacial movement.
Field identification & locations
Identify in the field by its hardness; it will easily scratch glass and steel. Look for a sugary, granular texture on broken surfaces. To distinguish from marble, apply a drop of vinegar; quartzite will not fizz. Common in mountain ranges and glacial deposits worldwide.
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