Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but iron staining often gives it tan, yellow, or reddish-brown hues; Luster: vitreous to waxy; Crystal structure: hexagonal/trigonal in origin but appears as a sugary, interlocking mosaic of grains; Cleavage: none (conchoidal or irregular fracture); Specific gravity: approximately 2.65.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, individual quartz grains recrystallize and fuse together. These rocks can date back from the Precambrian to more recent geological eras depending on regional tectonic history.

Uses & Applications

Used in construction as crushed stone for roadbeds, railway ballast, and roofing granules. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone in landscaping and architecture.

Geological Facts

Quartzite is so tough and durable that it often survives intense weathering better than the rocks around it, frequently forming the tops of ridges and resistant mountain peaks. It will scratch glass easily, distinguishining it from look-alike stones like limestone or marble.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, 'sugary' texture on fresh surfaces. Unlike sandstone, which breaks around grains, quartzite breaks through the grains. It is ubiquitous in mountainous regions and riverbeds worldwide.

Identified on: 4/13/2026

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