metamorphic
Quartzite River Cobble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Grayish-tan with hints of pink and yellow due to iron oxide staining. Luster: Dull to vitreous. Structure: Granular, non-foliated crystalline texture. Cleavage: None (breaks with conchoidal or irregular fracture).
- Hardness
- 7 on Mohs scale
- Luster
- Dull to vitreous
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale. Color: Grayish-tan with hints of pink and yellow due to iron oxide staining. Luster: Dull to vitreous. Structure: Granular, non-foliated crystalline texture. Cleavage: None (breaks with conchoidal or irregular fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to deep burial caused the quartz grains to recrystallize. This specific specimen has been rounded by fluvial (river) or glacial transport processes, likely over thousands of years.
Uses & applications
Industrial uses include crushed stone for road construction, railroad ballast, and as a source of silica for glass manufacturing. In a rounded cobble form, they are commonly used for xeriscaping, decorative gardening, and aquarium decoration.
Geological facts
Quartzite is so durable that it can outlast the mountains it formed in. Because it is harder than steel, it was sometimes used by prehistoric humans for stone tools when flint or chert was unavailable, though its granular nature makes it harder to flake.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and even a steel knife blade) and its smooth, water-worn exterior. These are extremely common in riverbeds, glacial tills, and along coastlines globally.
More like this
