sedimentary
Eurasite (or Ferruginous Sandstone)
Ferruginous Sandstone (SiO2 with Fe2O3/FeOOH)
Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, ochre; Luster: Dull/Earthy; Crystal Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.5-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark brown, reddish-brown, ochre
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark brown, reddish-brown, ochre; Luster: Dull/Earthy; Crystal Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.5-3.0
Formation & geological history
Formed through the cementation of quartz grains where iron oxides (hematite or goethite) act as the binding agent. The iron often leaches from surrounding soils into groundwater, precipitating in porous sand layers over millions of years.
Uses & applications
Primarily used as a minor building stone, decorative landscaping rock, and occasionally as a source of low-grade iron ore. In some regions, historical buildings were constructed from it due to its accessibility.
Geological facts
This specimen shows significant water-rolling or river tumbled wear, giving it a characteristic bread-loaf or bar shape. The dark, glossy 'patina' on the top surface is likely a desert varnish or water-deposited manganese/iron coating.
Field identification & locations
Identify in the field by its grainy sand-like texture, heavy weight compared to pure quartz, and reddish-brown streak. Often found in ancient riverbeds, coastal regions, and arid environments.
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