mineral

Ferruginous Quartz

Silicon Dioxide with Iron Oxide inclusions (SiO2 + Fe2O3/FeO(OH))

Hardness: 7 (Mohs scale); Color: Yellow, orange, reddish-brown, or rust-colored; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal prisms); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Yellow, orange, reddish-brown, or rust-colored
Luster: Vitreous to dull

Identified March 17, 2026More mineral →

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Physical properties

Formation & geological history

Formed in hydrothermal veins or as secondary deposits where silica-rich fluids permeate iron-rich environments. The iron oxide (limonite or hematite) coats the crystals or becomes included during growth. Age varies globally from Precambrian to recent epochs.

Uses & applications

Commonly used in lapidary work for cabochons, metaphysical collecting, and as landscape accents. Certain high-quality orange varieties are sold as 'Tangerine Quartz' in the gemstone market.

Geological facts

Also known as Eisenkiesel (German for 'iron pebble'). The staining is often just a microscopic layer on the surface, but it can also be distributed throughout the entire crystal, giving it a solid opaque orange color.

Field identification & locations

Identify in the field by its hexagonal crystal habit (if present), its ability to scratch glass (hardness 7), and its characteristic rust-like coloration. Found globally, especially in iron-mining regions like Brazil, Morocco, and the Great Lakes region of the USA.

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