metamorphic
Quartzite Pebble (with possible inclusion)
Metamorphosed Quartz Sandstone (SiO2 with impurities)
Hardness: 7 on Mohs scale; Color: Tan, beige, and light brown with iron staining; Luster: Waxy to dull (smoothed by water); Crystal structure: Microcrystalline quartz; Cleavage: None, exhibits conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, and light brown with iron staining
- Luster
- Waxy to dull (smoothed by water)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, and light brown with iron staining; Luster: Waxy to dull (smoothed by water); Crystal structure: Microcrystalline quartz; Cleavage: None, exhibits conchoidal or irregular fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure caused tectonic recrystallization of sand grains. This specific specimen has been further shaped by fluvial (river) or glacial transport, resulting in its rounded 'river rock' geometry.
Uses & applications
Used in landscaping, construction as aggregate, and occasionally tumbled for decorative crafts or aquariums. High-purity quartzite is used in glassmaking and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock during erosion, which is why it is commonly found as rounded pebbles in riverbeds and on beaches. The indentation in the center may be a weathered out mineral inclusion or a trace fossil impression.
Field identification & locations
Identifiable by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary appearance under magnification. Commonly found in areas with ancient mountain belts or glacial deposits.
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