metamorphic
Ferruginous Quartzite (also known as Ironstone or Gossan)
Ferruginous Quartzite with Goethite/Hematite staining
Hardness: 7 (Quartz component); Color: Gray to brownish-red; Luster: Dull to sub-vitreous; Structure: Massive or granular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 3.4 (depending on iron content)
- Hardness
- 7 (Quartz component)
- Color
- Gray to brownish-red
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 7 (Quartz component); Color: Gray to brownish-red; Luster: Dull to sub-vitreous; Structure: Massive or granular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 3.4 (depending on iron content)
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstones that were subsequently infiltrated or associated with iron oxides. The reddish staining suggests secondary oxidation (weathering) of iron-bearing minerals.
Uses & applications
Primary source for iron ore if found in large deposits (as BIFs); used in road construction and as decorative garden stone; used by prospectors as an indicator of potential mineralization nearby.
Geological facts
Rocks like this are often found by gold prospectors because iron oxides frequently occur in the same hydrothermal veins as gold. The rusty appearance is often referred to as 'gossan' or 'iron hat' by miners.
Field identification & locations
Identify in the field by its high hardness (won't be scratched by steel) and the characteristic rusty-orange or deep red staining. It is often heavier than standard quartz or granite. Commonly found in ancient shield areas and near mining districts.
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