metamorphic
Quartzite Cobble / Quartzite Pebble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to light brown (iron-stained); Luster: Vitreous to dull/waxy when weathered; Structure: Granofelsic (interlocking quartz grains); Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan to light brown (iron-stained)
- Luster
- Vitreous to dull/waxy when weathered
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to light brown (iron-stained); Luster: Vitreous to dull/waxy when weathered; Structure: Granofelsic (interlocking quartz grains); Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz sand grains recrystallize and fuse together. This specimen shows river or beach tumbling, indicating it was eroded from parent bedrock and smoothed by water over thousands of years.
Uses & applications
Used in heavy construction as road ballast, railway ballast, and in concrete aggregate. Crushed quartzite is used in glass making and industrial abrasives. High-purity quartzite is a source of silicon for electronic components.
Geological facts
Quartzite is so durable that it can survive surface weathering longer than most other rocks, often forming the 'caps' of mountain ranges. Because it is harder than steel, it was historically used by prehistoric humans to create stone tools when flint or chert was unavailable.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, 'sugary' texture visible on broken surfaces. This specimen is a common beach find in glaciated or mountainous regions. Collectors look for unique colors or 'ventifacts' (wind-sculpted shapes).
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