Ferruginous Quartz on Ironstone

Physical Properties

Hardness: 7 (Quartz) to 5.5-6.5 (Ironstone matrix); Color: Rusty brown, dark grey, and translucent white; Luster: Vitreous to sub-metallic; Crystal Structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal.

Formation & Geological History

Formed through the metamorphism of iron-rich sedimentary rocks (like Banded Iron Formations) where quartz veins precipitated from hydrothermal fluids in fractures.

Uses & Applications

Primarily used as iron ore in industry if iron content is high enough; also used for landscaping, geological teaching specimens, and minor lapidary work.

Geological Facts

The reddish-brown staining is caused by the oxidation of iron (rusting), which occurs when the rock is exposed to air and water. This process can happen over millions of years or relatively quickly on exposed surfaces.

Field Identification & Locations

Identify by its high density (heaviness), magnetic response (in some cases), and the presence of hard, crystalline quartz veins cutting through a darker, metallic or earthy matrix.

Identified on: 4/24/2026

Mode: Standard