metamorphic
Quartzite (River Pebble)
Quartzite (composed primarily of Silica, SiO2)
Hardness: 7 (Mohs scale); Color: Yellow-tan, honey-colored, or white due to iron oxide staining; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-tan, honey-colored, or white due to iron oxide staining; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the original quartz grains to recrystallize and fuse together. This specific specimen has been further shaped and polished by fluvial (river) erosion.
Uses & applications
Used in construction as crushed stone or ballast. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. Water-worn pebbles are popular in landscaping and home decor.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges in which it is formed. It is frequently mistaken for quartz crystals or agate, but its granular texture (resembling sugar under a magnifying glass) identifies it as a metamorphic rock.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its tendency to break across sand grains rather than around them. Common in riverbeds and glacial deposits worldwide. Collectors should look for unique translucency when held to a light.
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