metamorphic
Quartzite (Yellow/Tan Quartz Cobble)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on the Mohs scale. Color: Tan, yellow-brown, or honey-gold. Luster: Vitreous to waxy, especially when weathered or polished. Crystal structure: Hexagonal (microcrystalline/polycrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Tan, yellow-brown, or honey-gold
- Luster
- Vitreous to waxy, especially when weathered or polished
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Physical properties
Hardness: 7 on the Mohs scale. Color: Tan, yellow-brown, or honey-gold. Luster: Vitreous to waxy, especially when weathered or polished. Crystal structure: Hexagonal (microcrystalline/polycrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, original sand grains recrystallize into a dense, interlocking mosaic of quartz crystals. Specimen appears to be a river-worn or glacially-rounded cobble from the Phanerozoic era.
Uses & applications
Used in construction as crushed stone or road ballast, as a decorative landscape stone, and occasionally in glassmaking if pure. Smooth specimens are popular for rock tumbling and as 'worry stones' for collectors.
Geological facts
Quartzite is one of the most durable rocks on Earth's surface. It is often harder and more resistant to chemical weathering than the parent sandstone, meaning it frequently forms the caprock of ridges and mountains.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass and steel) and its granular, 'sugary' texture visible under a loupe. Commonly found in riverbeds, glacial tills, and mountainous regions like the Appalachians or the Scottish Highlands. Look for its translucent edges.
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