geigerite
{{Short description|Mineral}}
{{Infobox mineral
| name = Geigerite
| category = Arsenate minerals
| formula = Mn5(AsO3OH)2(AsO4)2·10H2O
| molweight = 1,012.54 g/mol
| strunz = 8.CE.05
| system = Triclinic
| class = Pinacoidal ({{overline|1}})
(same H-M symbol)
| symmetry = P{{overline|1}}
| unit cell = a = 7.94 Å, b = 10.69 Å
c = 6.77 Å; α = 80.97°
β = 84.2°, γ = 81.85°; Z = 1
| color = Red, colorless
| habit = Platy, partly triangular crystals to 0.5 mm
| cleavage = Perfect
| tenacity = brittle
| mohs = 3
| luster = Vitreous – pearly
| opticalprop = Biaxial (−)
| refractive = nα = 1.601 nβ = 1.630 nγ = 1.660
| birefringence = δ = 0.059
| pleochroism = Very weak, colorless to rose-red
| 2V = 89°
| streak = White
| gravity = 3.05
| diaphaneity = Transparent to translucent
| references = [http://webmineral.com/data/Geigerite.shtml Geigerite data on Webmineral.com][http://www.mindat.org/min-1669.html Geigerite on Mindat.org][http://rruff.geo.arizona.edu/doclib/hom/geigerite.pdf Geigerite in the Handbook of Mineralogy]
}}
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.
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.{{cite thesis |first=Thomas |last=Geiger |type=Ph.D. |year=1948 |title=Manganerze in der Radiolariten Graubündens |publisher=ETH Zürich |url=http://e-collection.library.ethz.ch/eserv/eth:21226/eth-21226-01.pdf}}
Composition
The chemical composition of geigerite is hydrous manganese arsenate (Mn5(AsO3OH)2(AsO4)2·10H2O). The chemical composition was found by using an electron microprobe in the Falotta mines in Switzerland.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.
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. Recently, geigerite has been found in Fukushima Prefecture, Japan.Kato et al. (1990) Ganseki-Koubutsu-Koshogaku Zasshi, 85, 184.; Mineralogical Journal Vol. 18 (1996), No. 4 pp 155–160 Geigerite has also been found in Mt. Nero Mine, Borghetto Di Vara, La Spieza, Italy.Cabella, R. (2000) Geigerite from Mt Nero manganese mine (Northern Apennines, La Spezia, Italy). Neues Jahrbuch fur Mineralogy-Monatshefte, 570–576.
Structure
Geigerite’s crystal system is triclinic with perfect cleavage on the {010}. The Herman Mauguin symbol for geigerite is {{overline|1}} and its space group is P{{overline|1}}. 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
See also
References
{{Reflist}}
- Bergknappe (2000) Verein der Freunde des Bergbaus in Graubunden Stiftung Bergbaumuseum Graubunden Schelzboden-Davos. 31–32.
{{Manganese minerals}}