Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: White to tan/brown (iron-stained), Luster: Vitreous to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal to irregular fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse into a dense, interlocking matrix. This process occurs during mountain-building events in various geological eras.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce glass and silicon metal. It is also used for decorative stone and countertops.

Geological Facts

Quartzite is so hard and durable that it often forms the resistant caps of mountain ridges. Unlike sandstone, which breaks around its individual grains, quartzite is so well-fused that it breaks directly through the quartz grains.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass and stainless steel) and its sugary, crystalline texture. It is commonly found in metamorphic terranes worldwide, such as the Appalachian Mountains or the Alps.

Identified on: 4/20/2026

Mode: Standard