Geigerite

Geigerite is a mineral, a complex hydrous manganese arsenate with formula: Mn₅(AsO₃OH)₂(AsO₄)₂·10H₂O. It forms triclinic pinacoidal vitreous colorless, red to brown crystals. It has a Mohs hardness of 3 and a specific gravity of 3.05.

It was discovered in Grischun, Switzerland in 1989. It was named in honor of Dr. Thomas Geiger (1886–1976), Wiesendangen, Switzerland, who studied the Falotta manganese ores.

Geigerite
General
Category	Manganese minerals
Chemical formula	Mn5(AsO3OH)2(AsO4)2·10H2O
Identification
Molar mass	1,012.54 gm
Color	Red, Colorless.
Crystal habit	Platy, partly triangular crystals to 0.5mm
Crystal system	Triclinic
Cleavage	Perfect
Tenacity	brittle
Mohs scale hardness	3 - Calcite
Luster	Vitreous - Pearly
Streak	white
Diaphaneity	Transparent to Translucent
Density	3.05
Pleochroism	very weak,colorless to rose-red
References

Composition

The chemical composition of geigerite is hydrous manganese arsenate or Mn5 (AsO4)2(AsO3OH)2 *10H20 (Graeser, S. 1989). The chemical composition was found by using an electron microprobe in the Falotta mines in Switzerland (Graeser, S. 1989).

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 crystal. Geigerite is then formed by metamorphism of manganese oxide ores (Graeser, S. 1989). Recently, geigerite has been found in Fukushima, Japan, in the Tohoku Region( Kato et al 1990). Geigerite has also been found in Mt. Nero Mine, [[Borghetto Di Vara]], La Spieza, Italy (Bella, R. 2000). Besides these three locations, geigerite has yet to be discovered anywhere else in the world.

Structure

Geigerite’s crystal system is triclinic with perfect cleavage on the {010}. The [[Herman Mauggin symbol]] for geigerite is *1 and its space group is P*I. 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. (Graeser, S. 1989)

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 (Graeser, S. 1989). 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 (Hybler M. 2003)

See also

• List of minerals
• List of minerals named after people

References

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

• Cabella, R. (2000) Geigerite from Mt Nero manganese mine (Northern Apennines, La Spezia, Italy). Neues Jahrbuch fur Mineralogy-Monatshefte, 570-576.

• Graeser, S.; Schwander, H.; Bianchi, R.; Pilati, T.; Gramaccioli, C. M. (1989): Geigerite, the manganese analogue of chudobaite: Its description and crystal structure. American Mineralogist: 74, 676-684.

• 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.

• Kato et al (1990) Ganseki-Koubutsu-Koshogaku Zasshi, 85, 184.; Mineralogical Journal Vol. 18 (1996) , No. 4 pp 155-160

• Mindat Home Page." Mineralogy Database - Mineral Collecting, Localities, Mineral Photos and Data. Web. 23 Oct. 2011. < http://www.mindat.org/min-1669.html>