Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, can be tinged by iron; Luster: Vitreous (glassy) to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, typically in orogenic (mountain-building) belts.

Uses & Applications

Used in construction as crushed stone or decorative dimension stone, as a source for silica in glassmaking, and in metallurgy. High-purity specimens are used in the electronics industry.

Geological Facts

Quartzite is so tough and resistant to chemical weathering that it often forms the ridges and peaks of mountain ranges. It is one of the hardest and most durable common rocks.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that sparkles under light. It breaks through the grains rather than around them, unlike sandstone.

Identified on: 4/16/2026

Mode: Standard