Quartzite with Iron Hydroxide Staining

Physical Properties

Hardness: 7 (Mohs scale), Color: Rusty brown, orange, and tan exterior due to iron oxide; Luster: Dull/earthy exterior; Crystal structure: Granular/Microcrystalline; Specific gravity: approx. 2.6

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone under high heat and pressure, causing the quartz grains to recrystallize into a dense, interlocking matrix. The surface coloring results from secondary weathering and the oxidation of iron-bearing minerals in soil or water.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and occasionally as decorative garden stones. High-purity quartzite is used to produce glass and silicon metal.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock layers, forming spectacular ridges and mountain peaks. This specific specimen’s 'rusty' look is a result of it being weathered in an environment rich in iron and oxygen.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture when freshly broken. Found globally, especially in old mountain belts and riverbeds as rounded cobbles.

Identified on: 4/26/2026

Mode: Standard