Rock Identifier
Gossan (Iron Hat) with Quartz and Chlorite (Limonite/Goethite-rich Gossan (FeO(OH)·nH2O) with inclusions of Quartz and Chlorite) — Mineral/Metamorphic Substrate
Mineral/Metamorphic Substrate

Gossan (Iron Hat) with Quartz and Chlorite

Limonite/Goethite-rich Gossan (FeO(OH)·nH2O) with inclusions of Quartz and Chlorite

Hardness: Variable (Quartz 7, Iron oxides 5-5.5); Color: Rusty red, earthy brown, with green chlorite and translucent quartz; Luster: Earthy to vitreous; Structure: Massive/amorphous iron oxides with crystalline inclusions; Cleavage: None/unpredictable.

Hardness
Variable (Quartz 7, Iron oxides 5-5
Luster
Earthy to vitreous
Identified More mineral/metamorphic substrate →

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Physical properties

Hardness: Variable (Quartz 7, Iron oxides 5-5.5); Color: Rusty red, earthy brown, with green chlorite and translucent quartz; Luster: Earthy to vitreous; Structure: Massive/amorphous iron oxides with crystalline inclusions; Cleavage: None/unpredictable.

Formation & geological history

Formed through the intense oxidation of sulfide ore deposits near the surface (the 'iron hat'). Rainwater reacts with mineral sulfides like pyrite, leaching away metals and leaving behind stable iron oxides, quartz, and secondary minerals like chlorite.

Uses & applications

Historically used as an indicator for miners to find deeper deposits of copper, gold, or silver. Today, primarily collected as geological specimens or used as low-grade iron ore in specific contexts.

Geological facts

Gossans are essentially 'rotted' rock. In many famous gold rushes, miners first discovered these rusty outcrops because the oxidation process often concentrates heavy gold particles as other minerals weather away.

Field identification & locations

Identify in the field by its distinct rusty, 'burnt' appearance and porous texture compared to surrounding rock. Common in old mining districts or areas with hydrothermal activity. Collectors look for unique mineral inclusions within the iron matrix.

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Other mineral/metamorphic substrate specimens

Quartzite River Pebble (Quartzite (primarily SiO2)) — metamorphic

Quartzite River Pebble

Quartzite (primarily SiO2)

metamorphic
Quartzite Pebbles (Meta-quartzite (SiO2)) — metamorphic

Quartzite Pebbles

Meta-quartzite (SiO2)

metamorphic
Mixed Tumbled Gemstones and River Rocks (Mixed Decorative Stones (predominantly Silicon Dioxide - SiO2 variants)) — Mixed (Igneous, Sedimentary, Metamorphic, and Minerals)

Mixed Tumbled Gemstones and River Rocks

Mixed Decorative Stones (predominantly Silicon Dioxide - SiO2 variants)

Mixed (Igneous, Sedimentary, Metamorphic, and Minerals)
River Pebble (Likely Quartzite or Chert) (Quartzite (primarily SiO2)) — metamorphic

River Pebble (Likely Quartzite or Chert)

Quartzite (primarily SiO2)

metamorphic
Pyrite (on a metal substrate) (Iron Sulfide (FeS2)) — mineral

Pyrite (on a metal substrate)

Iron Sulfide (FeS2)

mineral
River Stone (likely Quartzite or Chert) (Recrystallized Silicon Dioxide (SiO2)) — metamorphic

River Stone (likely Quartzite or Chert)

Recrystallized Silicon Dioxide (SiO2)

metamorphic