metamorphic
Quartzite (River Pebble)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, off-white, to beige with sugary texture; Luster: Dull to vitreous; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.63 - 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, off-white, to beige with sugary texture
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, off-white, to beige with sugary texture; Luster: Dull to vitreous; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.63 - 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in convergent plate boundaries. This specific specimen has been further shaped by fluvial (river) erosion over thousands of years.
Uses & applications
Used as a high-quality decorative aggregate in landscaping, as a building stone, and in the production of glass or silicon. Often used as ballast for railroads.
Geological facts
Quartzite is so hard that it will scratch steel and glass easily. Unlike sandstone, when quartzite is broken, it fractures through the individual sand grains rather than around them due to the intense pressure that fused the silica.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife) and its grainy, sugary surface texture. Common in riverbeds and glacial deposits globally. Collectors should look for unique banding or internal translucent clarity.
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