Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Grayish-tan with reddish-brown iron staining; Luster: Vitreous/waxy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Density: ~2.65 g/cm³.

Formation & Geological History

Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together. Often found in Precambrian or Paleozoic metamorphic belts.

Uses & Applications

Used in construction as crushed stone for road beds, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial ceramics.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of hills and ridges. It is frequently mistaken for sandstone, but unlike sandstone, it will break through the grains rather than around them.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through sand grains rather than around their boundaries. Common in mountain ranges and riverbeds downstream from metamorphic outcrops.

Identified on: 4/27/2026

Mode: Standard