Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, brown, or light reddish-brown (likely due to iron oxide staining); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the individual quartz grains to recrystallize and fuse together into a dense, hard rock.

Uses & Applications

Used extensively in road construction, as railroad ballast, for kitchen countertops due to its hardness, and occasionally for decorative stone or jewelry when it contains colorful inclusions.

Geological Facts

Quartzite is so hard that it will scratch glass and steel. It is much more durable than its parent rock, sandstone, and is highly resistant to chemical weathering, often forming prominent ridges or mountain peaks.

Field Identification & Locations

Identify in the field by its grainy, sandpaper-like surface that nonetheless breaks through the sand grains rather than around them. It is very difficult to break even with a rock hammer. Found globally in ancient tectonic plate boundaries.

Identified on: 5/1/2026

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