Limonite-stained Quartz / Quartzite

Physical Properties

Hardness: 7 (Mohs); Color: Tan/yellowish-brown due to iron oxidation; Luster: Dull/waxy (unpolished) to vitreous; Crystal Structure: Trigonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65.

Formation & Geological History

Formed through the accumulation of quartz-rich sand and subsequent cementation or low-grade metamorphism. The yellow/brown staining occurs via secondary weathering where iron minerals oxidize into limonite or goethite, permeating the porous surface of the rock.

Uses & Applications

Common quartzites are used in construction for road ballast and dimension stone. Stained specimens are occasionally used in 'river rock' landscaping or as decorative pebbles.

Geological Facts

Quartz is one of the most chemically stable minerals on Earth's surface. The yellow coloring is essentially 'stone rust,' where iron-rich water has interacted with the silica over long periods of time.

Field Identification & Locations

Identify by its hardness (will scratch glass), lack of visible grains (unlike sandstone), and its resistance to acid (unlike limestone). It is commonly found in riverbeds, glacial tills, and weathered outcrops globally.

Identified on: 4/17/2026

Mode: Standard