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Geigerite
Mineral From Wikipedia, the free encyclopedia
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Geigerite is a mineral, a complex hydrous manganese arsenate with formula: Mn5(AsO3OH)2(AsO4)2·10H2O. It forms triclinic pinacoidal, vitreous, colorless to red to brown crystals. It has a Mohs hardness of 3 and a specific gravity of 3.05.[2][3]
It was discovered in Grischun, Switzerland in 1989. It was named in honor of Thomas Geiger (1886–1976), Wiesendangen, Switzerland, who studied the Falotta manganese ores.[5][6]
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Composition
The chemical composition of geigerite is hydrous manganese arsenate (Mn5(AsO3OH)2(AsO4)2·10H2O).[4] The chemical composition was found by using an electron microprobe in the Falotta mines in Switzerland.[4]
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.[4] Recently, geigerite has been found in Fukushima Prefecture, Japan.[7] Geigerite has also been found in Mt. Nero Mine, Borghetto Di Vara, La Spieza, Italy.[8]
Structure
Geigerite’s crystal system is triclinic with perfect cleavage on the {010}. The Herman Mauguin symbol for geigerite is 1 and its space group is P1.[2] 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.[4]
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.[4] 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.[9]
See also
References
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