Geigerite

Composition

The chemical composition of geigerite is hydrous manganese arsenate (Mn5(AsO3OH)2(AsO4)2·10H2O).

Geologic occurrence

Geigerite can be found in the abandoned manganese mine in Oberhalbstein, Switzerland. It is mainly found in cavities in adiolarites, which are a form of igneous rock that have either a radial or fanlike texture of crystals. Geigerite is then formed by metamorphism of manganese oxide ores. Geigerite has also been found in Mt. Nero Mine, Borghetto Di Vara, La Spieza, Italy.

Structure

Geigerite’s crystal system is triclinic with perfect cleavage on the {010}. The Herman Mauguin symbol for geigerite is and its space group is P. Geigerite contains two arsenate ions which are independent of one another. The first is the AsO3OH group, and the second is the AsO4. In the acidic AsO3OH group, the As-O bonds are much shorter than the As-OH bonds. Similarly, in the AsO4 group, As-O bonds are also shorter than the As-O bonds. The remaining bonds within both arsenate groups have nearly equal distances. In the ions there are three manganese atoms, these three links to six oxygen atoms to form a normal octahedral formation.

Special characteristics

One interesting structural feature of geigerite is the presence of a complicated network of hydrogen bonds, which exceed the number of the hydrogen atoms. Geigerite is classified under a group of metal copper (II) arsenates called the Lindackerite group. Minerals within this group have a formula where M equals either copper, calcium, manganese, zinc, or cobalt.

References

• Bergknappe (2000) Verein der Freunde des Bergbaus in Graubunden Stiftung Bergbaumuseum Graubunden Schelzboden-Davos. 31–32.

References

1. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
2. [http://webmineral.com/data/Geigerite.shtml Geigerite data on Webmineral.com]
3. [http://www.mindat.org/min-1669.html Geigerite on Mindat.org]
4. [http://rruff.geo.arizona.edu/doclib/hom/geigerite.pdf Geigerite in the Handbook of Mineralogy]
5. Geiger, Thomas. (1948). "Manganerze in der Radiolariten Graubündens". ETH Zürich.
6. Cabella, R. (2000) Geigerite from Mt Nero manganese mine (Northern Apennines, La Spezia, Italy). Neues Jahrbuch fur Mineralogy-Monatshefte, 570–576.
7. Hybler, M. (2003) Crystal structure of Lindackerite, (Cu,Co,Ni)CU4(AsO4)(2)(AsO3OH)(2)center dot 9 H2O from Jachymov, Czech republic. European Journal of Mineralogy, 1035–1042.