metamorphic
Quartzite Pebbles
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron staining can cause reddish-brown tones); Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline/interlocking grains); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron staining can cause reddish-brown tones); Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline/interlocking grains); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, original quartz grains recrystallize and fuse together. These specimens are water-worn river or beach pebbles, likely polished by transport over thousands of years.
Uses & applications
Industrial uses include glassmaking and as an abrasive. In construction, crushed quartzite is used for road ballast and decorative landscaping. High-quality pieces are used for countertops or as garden ornaments.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was formed in, becoming the primary component of gravel deposits and river beds long after softer rocks have eroded away. It is significantly harder than the sandstone it originates from.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its lack of reaction to acid (unlike marble). These specimens show characteristic rounding and smoothing from fluvial or coastal erosion. Common in glaciated regions and river basins.
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