Quartz / Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: White to translucent gray with iron staining; Luster: Vitreous to waxy; Structure: Crystalline but often appears massive in field specimens; Cleavage: None (conchoidal fracture); SG: 2.65.

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. It can be found in various geological ages, often in orogenic (mountain-building) belts.

Uses & Applications

Used primarily in construction as crushed stone or aggregate. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon. It is also common in landscaping.

Geological Facts

Quartzite is so tough that it often outlasts the mountains it forms; it usually breaks through the quartz grains rather than around them, unlike sandstone. It is one of the most chemically resistant rocks on the Earth's surface.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass or steel) and its grainy, sandpaper-like texture that has been 'fused' together. It lacks the fizzing reaction to acid seen in marble.

Identified on: 4/15/2026

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