Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline grains); No cleavage; Specific gravity 2.6-2.7.

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together, creating a hard, interlocking structure. It is found in mountain belts worldwide.

Uses & Applications

Used as crushed stone in road construction, railroad ballast, and building stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics. Smooth cobbles are popular in landscaping.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than the rocks surrounding it, forming prominent ridges and peaks in many mountain ranges. It can be distinguished from sandstone because it breaks across grain boundaries rather than around them.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and sandy, sugary texture on fresh breaks. It is commonly found in riverbeds as rounded cobbles or in craggy mountain outcrops.

Identified on: 4/20/2026

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