Quartzite

Hardness: 7 (Mohs scale), Color: White/Gray, Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None/Conchoidal fracture, Specific gravity: 2.65

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic. Found in orogenic belts and tectonic plate boundaries.

Used extensively in road construction, as railway ballast, in the manufacture of glass and ceramics, and as a decorative building stone or countertop material.

Quartzite is so hard and chemically resistant that it often forms prominent ridges and resistant mountain peaks. It will scratch steel and glass easily.

Identified in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture that resembles sandstone but lacks the porosity. Common globally in crystalline basement complexes.