sedimentary
Ferruginous Sandstone (Gozzan)
Iron-rich clastic sedimentary rock with Limonite/Goethite
Hardness: 5-6 (Mohs); Color: Dark brown, grey, and rusty orange; Luster: Dull to earthy; Texture: Granular and vesicular with oxidation crusts; Specific Gravity: 2.8-3.5
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown, grey, and rusty orange
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown, grey, and rusty orange; Luster: Dull to earthy; Texture: Granular and vesicular with oxidation crusts; Specific Gravity: 2.8-3.5
Formation & geological history
Formed through the secondary enrichment of iron oxides within a sedimentary matrix, or as a cap (gossan) over mineral deposits where sulfides have been leached away by weathering. It represents the oxidation of iron-bearing minerals over thousands of years.
Uses & applications
Primarily used as an indicator for metal prospecting (gold, copper, silver) in mining. In construction, it is sometimes used as low-grade road metal or fill.
Geological facts
This material is often called a 'gossan' or 'iron hat' by miners. It forms the upper portion of a mineral vein and was historically used by prospectors as a 'signpost' for finding underlying precious metal ores.
Field identification & locations
Identify by its high density compared to normal sandstone, rusty staining, and vuggy (cavitous) texture. Commonly found in arid mining districts like Arizona, Australia, or South Africa. Use a streak test; it will usually leave a yellow-brown mark.
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