metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white to tan with heavy iron-oxide (rust) staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); High specific gravity (2.6-2.7).
- Hardness
- 7 on Mohs scale
- Color
- white to tan with heavy iron-oxide (rust) staining
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: white to tan with heavy iron-oxide (rust) staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); High specific gravity (2.6-2.7).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together. This specific specimen has been rounded and weathered by water transportation (fluvial processes).
Uses & applications
Primarily used in construction as crushed stone or road ballast. High-purity quartzite is used in glassmaking and to produce silicon metal. As a cobble, it is common in landscaping.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion, outlasting the softer rocks around it. The brown and orange coloring on this specimen is due to limonite or hematite staining from groundwater interaction.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary texture. Found globally in riverbeds, glacial deposits, and sedimentary basins where older metamorphic rock has eroded.
