Geigerite
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.[1][2]
| Geigerite | |
|---|---|
| General | |
| Category | Arsenate minerals |
| Formula (repeating unit) | Mn5(AsO3OH)2(AsO4)2·10H2O |
| Strunz classification | 8.CE.05 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (same H-M symbol) |
| Space group | P1 |
| 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 |
| Identification | |
| Formula mass | 1,012.54 g/mol |
| Color | Red, colorless |
| Crystal habit | Platy, partly triangular crystals to 0.5 mm |
| Cleavage | Perfect |
| Tenacity | brittle |
| Mohs scale hardness | 3 |
| Luster | Vitreous - pearly |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.05 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.601 nβ = 1.630 nγ = 1.660 |
| Birefringence | δ = 0.059 |
| Pleochroism | Very weak, colorless to rose-red |
| 2V angle | 89° |
| References | [1][2][3][4] |
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.[4][5]
Composition
The chemical composition of geigerite is hydrous manganese arsenate (Mn5(AsO3OH)2(AsO4)2·10H2O).[3] The chemical composition was found by using an electron microprobe in the Falotta mines in Switzerland.[3]
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.[3] Recently, geigerite has been found in Fukushima Prefecture, Japan.[6] Geigerite has also been found in Mt. Nero Mine, Borghetto Di Vara, La Spieza, Italy.[7]
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.[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.[3]
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.[3] 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.[8]
See also
References
- Geigerite data on Webmineral.com
- Geigerite on Mindat.org
- 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.
- Geigerite in the Handbook of Mineralogy
- Geiger, Thomas (1948). Manganerze in der Radiolariten Graubündens (PDF) (Ph.D.). ETH Zürich.
- Kato et al. (1990) Ganseki-Koubutsu-Koshogaku Zasshi, 85, 184.; Mineralogical Journal Vol. 18 (1996), No. 4 pp 155-160
- Cabella, R. (2000) Geigerite from Mt Nero manganese mine (Northern Apennines, La Spezia, Italy). Neues Jahrbuch fur Mineralogy-Monatshefte, 570-576.
- 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.
- Bergknappe (2000) Verein der Freunde des Bergbaus in Graubunden Stiftung Bergbaumuseum Graubunden Schelzboden-Davos. 31-32.