Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous to dull; Crystal Structure: non-foliated, granular; Cleavage: none, breaks with conchoidal fracture; Specific gravity: approx. 2.65.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. This recrystallization process interlocks the quartz grains into a very dense rock. It can range from Precambrian to much younger geological ages.

Uses & Applications

Used primarily in construction for crushed stone, road ballast, and decorative building stone. Highly pure quartzite is used to produce silica sand for glassmaking and industrial abrasives.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding softer rocks during erosion, frequently forming the peaks of ridges and mountains. It is often mistaken for marble, but can be distinguished by its superior hardness.

Field Identification & Locations

Identify in the field by its hardness (it will easily scratch glass) and lack of reaction to acid. Commonly found in folded mountain ranges and glacial deposits. Look for a sugary, granular texture on fresh surfaces.

Identified on: 5/3/2026

Mode: Standard