Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, can be reddish-brown from iron; Luster: vitreous to dull; Crystal structure: non-clastic, interlocking grains; Specific gravity: approx. 2.6

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone under extreme heat and pressure. Most specimens range from several hundred million to billions of years old, often found in mountain belts and shield areas.

Uses & Applications

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

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock, leading to it forming the heart of many mountain peaks and ridges. It is often confused with marble but can be distinguished because it will not react with acid.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass) and its grainy, granular look compared to chert. It is commonly found in riverbeds as rounded 'river rocks' or in large mountainous outcrops.

Identified on: 4/21/2026

Mode: Standard