metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to yellowish-brown due to iron staining; Luster: Vitreous to dull/granular; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6-2.7. It is extremely durable and hard.
- Hardness
- 7 on Mohs scale
- Color
- Tan to yellowish-brown due to iron staining
- Luster
- Vitreous to dull/granular
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to yellowish-brown due to iron staining; Luster: Vitreous to dull/granular; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6-2.7. It is extremely durable and hard.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific rounded cobble indicates a history of water erosion in a riverbed or glacial environment.
Uses & applications
Primarily used as crushed stone in road construction, railway ballast, and as a raw material for glass and ceramics. Smooth cobbles are popular in landscaping and decorative masonry.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It often maintains the granular texture of original sandstone but fractures through the grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and its grainy, sugary texture on freshly broken surfaces. Common in riverbeds and mountainous terrain globally.
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