Quartzite

Hardness of 7 on the Mohs scale, colors ranging from white and gray to pink, red, or purple due to iron impurities. It has a non-foliated structure, vitreous to dull luster, and breaks across quartz grains rather than around them.

Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during tectonic compression in orogenic belts. This metamorphic process fuses the quartz grains together into a dense, durable mass.

Used in construction, as crushed stone for road foundations, railway ballast, manufacturing of silica brick, and sometimes as a decorative dimension stone or countertop material.

Quartzite is extremely resistant to chemical weathering and erosion, which is why ridges formed of quartzite often persist as high mountain crests or prominent hills in the landscape.

Can be identified in the field by its extreme hardness (scratches glass easily and cannot be scratched by a knife) and the sugary texture of fractured surfaces where quartz grains are visible. Found globally in ancient mountain belts and regional metamorphic terranes.