Editorial Feature

Ahlfeldite – Occurrence, Properties, and Distribution

Jun 12 2014

Ahlfeldite was named after Friedrich E. Ahlfeld (1892–1982), a German–Bolivian mining engineer and mineralogist.

Properties of Ahlfeldite

The following are the key properties of Ahlfeldite:

Cell Data
- Space group: P2₁/n
- a = 7.53(1)
- b = 8.76(2)
- c = 6.43(1)
- β = 99°05 (15)’
- Z = 4

Crystal Data
- Monoclinic
- Point group: 2/m
- Rare crystals, to 1mm
- Elongated along [001] or flattened parallel {110}, showing {110}, {011}, {032}, {103}, {101}
- Crystalline crusts and spherical aggregates
- X-ray powder pattern: 5.69 (100), 3.426 (80), 2.992 (75), 2.190 (75), 3.772 (60), 2.719 (60), 2.354 (50)

Chemical Composition

Elements	Content 1	Content 2
SeO₂	50.01	50.03
NiO	30.24	16.84
H₂O	16.2	16.24
CoO	3.55	16.89
Total	100.0	100.00

Optical Properties
- Optical class: Biaxial (-)
- Pleochroism: X = pale green; Y = pale pink; Z = pink
- Orientation: Y = b; Z^c = -16°
- Dispersion: r < v, strong
- α = 1.709(1); β = 1.752(1); γ = 1.787(2)
- 2V(meas.) = 85°

Estimated Properties

Electron density	Bulk density (electron density) = 3.36 g/cm³ note: Specific gravity of ahlfeldite = 3.52 g/cm³
Photoelectric	PE_Ahlfeldite = 36.69 barns/electron U = PE_Ahlfeldite x ρ electron density = 123.20 barns/cm³
Fermion index	Fermion index = 0.02 Boson index = 0.98
Radioactivity	Ahlfeldite is not radioactive

How to Identify Ahlfeldite

Ahlfeldite 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.

Global Distribution

Ahlfeldite is mainly distributed in Bolivia - From the Pacajake mine, Hiaco, 24km east-north-east of Colquechaca; and the El Dragon mine, 30km south-west of Cerro Rico de Potosi, Potosi.

Occurrence of Ahlfeldite and Useful Mineral Association

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.