Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but iron oxides often give it a brown, tan, or reddish hue; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure. This causes the individual quartz grains to recrystallize and fuse together, creating a structure much denser and harder than the parent sandstone.

Uses & Applications

Used widely in construction for road ballast, roofing granules, and as a decorative stone. Because of its hardness, it has historically been used to make stone tools and is now popular in landscaping and as a countertop material.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges. Unlike sandstone, which breaks around its grains, quartzite breaks through the grains due to the intense fusion of the silica.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sugary appearance on fresh breaks. It is found globally in mountainous regions and areas with ancient tectonic activity.

Identified on: 4/15/2026

Mode: Standard