sedimentary
Ferruginous Sandstone
Arenite with limonite/goethite cement
Hardness: 6-7 (individual quartz grains), 2-3 (iron oxide matrix); Color: yellow, ochre, rusty brown; Luster: dull, earthy; Crystal structure: granular clastic texture; Specific gravity: 2.2-2.8
- Hardness
- 6-7 (individual quartz grains), 2-3 (iron oxide matrix)
- Color
- yellow, ochre, rusty brown
- Luster
- dull, earthy
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Physical properties
Hardness: 6-7 (individual quartz grains), 2-3 (iron oxide matrix); Color: yellow, ochre, rusty brown; Luster: dull, earthy; Crystal structure: granular clastic texture; Specific gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation of sand-sized minerals, mostly quartz, which are then cemented together by iron oxides (limonite or goethite) precipitated from groundwater. Commonly found in riverbeds, deltas, and arid basins.
Uses & applications
Historically used as a low-grade building stone and a pigment (ochre); occasionally used in landscaping or as a source of iron ore in primitive metallurgy.
Geological facts
The distinct yellow color is due to the presence of hydrated iron oxides. In some areas, these stones are referred to as 'ironstone' or 'yellow dog' in local vernacular.
Field identification & locations
Identified by its gritty, sand-paper like feel and its tendency to leave a yellowish streak on a streak plate. It is common in regions with heavily oxidized soil profiles.
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