Amargosite

Amargosite is an obsolete mineral name, historically used as a synonym for bentonite (a clay composed mainly of montmorillonite). It is not recognized today as a distinct mineral species by the International Mineralogical Association (IMA).

🌍 Origins and Naming

• Name Origin: Derived from the Amargosa region in Nevada, USA, where bentonite deposits occur.
• Status: Considered a synonym of bentonite rather than a valid mineral species.
• Historical Context: In older mineralogical references, “amargosite” was used to describe clay-rich bentonite deposits, but modern classification subsumes it under bentonite.

🔬 Chemical and Structural Properties (Bentonite / Montmorillonite)

• Formula: (Na,Ca)₀.₃₃(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O (generalized for montmorillonite).
• Mineral Group: Smectite clays.
• Crystal System: Monoclinic (but crystals are extremely small, often cryptocrystalline).
• Color: White, cream, gray, or pale green.
• Habit: Earthy, clay-like masses.
• Hardness: ~1–2 on Mohs scale.
• Specific Gravity: ~2.3–2.6.
• Special Property: High swelling capacity and cation-exchange ability due to its layered structure.

⚙️ Geological Occurrence

• Formation: Alteration of volcanic ash in sedimentary basins.
• Localities: Amargosa region (Nevada, USA), Wyoming, and worldwide bentonite deposits.
• Associated Minerals: Zeolites, feldspars, volcanic glass.

📖 Scientific and Industrial Significance

• Petrology: Important indicator of volcanic ash alteration.
• Industrial Uses (Bentonite):
  • Drilling muds in oil and gas exploration.
  • Foundry sands (binding agent).
  • Absorbents (cat litter, spill control).
  • Sealants for landfills and ponds.
  • Food and pharmaceutical uses (clarifying agents, detox clays).
• Collectors: Not collected as a mineral specimen; valued for industrial utility.

✨ Conclusion

Amargosite is simply an obsolete synonym for bentonite, a clay dominated by montmorillonite. While the name survives in historical references, modern mineralogy recognizes only bentonite as the correct term.

In short: Amargosite = old name for bentonite (montmorillonite-rich clay), not a valid mineral species today.

Sources: Mindat – Amargosite entry