Amarantite

Amarantite is a rare hydrated iron sulfate mineral with the formula Fe³⁺₂(SO₄)O·7H₂O. It is one of the more unusual secondary sulfates formed in oxidized environments, notable for its striking reddish coloration.

🌍 Origins and Naming

• Name Origin: From the Greek amarantos (“unfading”), referring to its persistent reddish color.
• Discovery: First described in 1850.
• Type Locality: Copiapó, Atacama Desert, Chile.

🔬 Chemical and Structural Properties

• Formula: Fe³⁺₂(SO₄)O·7H₂O
• Mineral Group: Sulfates.
• Crystal System: Monoclinic.
• Color: Bright red to reddish-brown.
• Habit: Acicular (needle-like) crystals, fibrous aggregates, crusts.
• Hardness: ~2 on Mohs scale (very soft).
• Specific Gravity: ~2.1–2.2 (light due to hydration).
• Luster: Vitreous to silky.
• Streak: Pale yellow to orange.

⚙️ Geological Occurrence

• Formation: Secondary mineral formed in the oxidation zones of pyrite and other iron sulfides.
• Environment: Found in arid climates where evaporation concentrates sulfate-rich solutions.
• Associated Minerals: Copiapite, coquimbite, halotrichite, melanterite, and other hydrated iron sulfates.
• Localities:
  • Copiapó, Chile (classic locality).
  • Other occurrences in arid mining districts worldwide.

📖 Scientific and Collector Significance

• Petrology: Indicator of highly oxidized, sulfate-rich environments.
• Collectors: Attractive red acicular crystals are prized, though delicate and unstable.
• Industrial Note: No commercial use; valued mainly for rarity and mineralogical interest.

✨ Conclusion

Amarantite is a rare red hydrated iron sulfate, first described from Chile. It forms delicate acicular crystals in oxidized sulfide deposits, serving as a vivid indicator of sulfate-rich environments but remaining a collector’s curiosity rather than an economic resource.

In short: Amarantite = Fe³⁺₂(SO₄)O·7H₂O, red hydrated iron sulfate, monoclinic, first found in Copiapó, Chile.