Köttigite
| Köttigite | |
|---|---|
Köttigite from Mapimí, Mexico
|
|
| General | |
| Category | Arsenate mineral |
|
Formula (repeating unit) |
Zn3(AsO4)2·8H2O |
| Strunz classification | 8.CE.40 (10 ed.) VII/C.13-90 (8 ed.) |
| Dana classification | 40.3.6.5 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| Identification | |
| Formula mass | 618.13 g/mol |
| Colour | Colourless, pink, red, red-orange or brown; light rose-pink in transmitted light |
| Crystal habit | Crystals prismatic [001] and flattened {010}. Also in crusts with a crystalline surface and fibrous structure |
| Cleavage | Perfect on {010} |
| Fracture | Fibrous fracture yields a silky lustre |
| Tenacity | Flexible |
| Mohs scale hardness | 2½ to 3 |
| Lustre | Resinous or waxy, silky on fracture |
| Streak | Reddish-white to white |
| Diaphaneity | Translucent |
| Specific gravity | 3.33 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.622, nβ = 1.638, nγ = 1.671 |
| Birefringence | δ = 0.049 |
| Pleochroism | Visible. X, Y = colourless, Z = pale red. |
| Solubility | Soluble in acids |
| Other characteristics | Not fluorescent |
| References | |
Köttigite is a rare hydrated zinc arsenate which was discovered in 1849 and named by James Dwight Dana in 1850 in honour of Otto Friedrich Köttig (1824 - 1892), a German chemist from Schneeberg, Saxony, who made the first chemical analysis of the mineral. It has the formula Zn3(AsO4)2·8H2O and it is a dimorph of metaköttigite, which means that the two minerals have the same formula, but a different structure: köttigite is monoclinic and metaköttigite is triclinic. There are several minerals with similar formulae but with other cations in place of the zinc. Iron forms parasymplesite Fe2+3(AsO4)2·8H2O; cobalt forms the distinctively coloured pinkish purple mineral erythrite Co3(AsO4)2·8H2O and nickel forms annabergite Ni3(AsO4)2·8H2O. Köttigite forms series with all three of these minerals and they are all members of the vivianite group.
The Vivianite Group is a group of monoclinic phosphates and arsenates with divalent cations. The group members are annabergite, arupite, babanekite, baricite, erythrite, hornesite, kottingite, manganhornesite, pakhomovskyite, parasymplesite and vivianite.
...
Wikipedia