Quartzite (Milky)

Physical Properties

Hardness: 7 (Mohs), Color: Milky white to light grey, Luster: Vitreous to waxy, Crystal Structure: Hexagonal/Trigonal system (granular texture in rock form), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. This process causes individual quartz grains to recrystallize into a locked, crystalline structure. Most deposits vary in age from Precambrian to more recent tectonic events.

Uses & Applications

Used as crushed stone for road construction and railway ballast; in manufacturing refractory bricks, glass, and ceramics; and occasionally for architectural stone and decorative gravel.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms prominent ridges and hills in landscapes, as it resists erosion much better than surrounding softer rocks.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often presents with a sugary, granular appearance but a smooth, glassy feel on fractured surfaces. Found globally in mountainous or metamorphic terranes.

Identified on: 4/18/2026

Mode: Standard