metamorphic

Weathered quartzite

Quartzite; predominantly recrystallized quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness about 7 Mohs; gray-tan, massive and fine- to medium-grained with sugary texture, vitreous to dull luster, and little or no cleavage. The irregular rusty-brown patches are likely iron-oxide staining along fractures or former bedding.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when quartz-rich sandstone was intensely metamorphosed and fused by heat and pressure, commonly during mountain building; its exact geological age cannot be determined from the image. Weathering has rounded the exposed surface.

Uses & applications

Used as crushed stone, aggregate, riprap, paving, wall stone, and occasionally countertops or architectural stone; this ordinary cobble has little jewelry value.

Geological facts

Quartzite commonly preserves faint sedimentary layering while being much harder and more resistant than its sandstone parent. It can resemble quartz-rich sandstone but usually breaks across grains rather than around them.

Field identification & locations

Common in metamorphic mountain belts worldwide, including the Appalachian, Rocky, and Precambrian shield regions. Field tests include scratching glass, resisting a steel knife, and showing little reaction to dilute hydrochloric acid; sandstone grains or weaker bedding suggest an incompletely metamorphosed rock.