Ahlfeldite, formula ((Ni,Co)[SeO3]·2H2O) is a mineral of secondary origin. It’s named after Friedrich Ahlfeld (1892–1982), a German-Bolivian mining engineer and geologist. Its type locality is Virgen de Surumi mine, Pakajake Canyon, Chayanta Province, Potosí Department, Bolivia.

General information

  • Category: Selenite mineral
  • Formula: (Ni,Co)SeO32H2O
  • Crystal system: Monoclinic
  • Crystal class: Prismatic (2/m)

Identify Ahlfeldite

It can be identified in the field by its color variations, such as pink, brown, apple-green, and red. Its transparent form has {110} distinct, {103} distinct cleavage. This mineral has a vitreous luster, with a light green streak. The fracture on this mineral is brittle.

The density of ahlfeldite is 3.37 g/cm3, with a hardness of 2 to 2.5 – between gypsum and finger nail.

Physical Properties of Ahlfeldite

  • Cleavage: {110} Distinct, {103} Distinct
  • Color: Pink brown, Apple green, Red.
  • Density: 3.37
  • Diaphaneity: Transparent
  • Fracture: Brittle – Generally displayed by glasses and most non-metallic minerals.
  • Habit: Prismatic – Crystals Shaped like Slender Prisms (e.g. tourmaline).
  • Hardness: 2-2.5 – Gypsum-Finger Nail
  • Luster: Vitreous (Glassy)
  • Streak: light green

Occurrence and Usefulness

Ahlfeldite occurs in a rare alteration product of nickel-bearing selenides and sulfides. It is often associated with minerals such as penroseite, olsacherite, chalcomenite, cerussite, anglesite, goethite, chalcomenite, olsacherite, and lepidocrocite.


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