| Posnjakite | |
| Category: | Copper minerals |
| Formula: | Cu4[(OH)<sub>6</sub>{{Pipe}}SO<sub>4</sub>] • H2O |
| Imasymbol: | Pnk[1] |
| Molweight: | 488.32 g/mol |
| Strunz: | 7.DD.10 |
| Dana: | 31.4.1.1 |
| System: | Monoclinic |
| Class: | Domatic (m) (same H-M symbol) |
| Symmetry: | Pa |
| Unit Cell: | a = 10.578 Å, b = 6.345 Å, c = 7.863 Å; β = 117.98°; Z = 2[2] |
| Color: | Sky-blue to dark-blue |
| Habit: | Crystals scaly, or as crusts; earthy |
| Mohs: | 2 to 3 |
| Luster: | Vitreous |
| Refractive: | nα = 1.625 nβ = 1.680 nγ = 1.706 |
| References: | [3] |
Posnjakite is a hydrated copper sulfate mineral. It was discovered in the Tungsten deposit of Nura-Taldy[4] in Karaganda Region in Kazakhstan and described in 1967 by Aleksandr Ivanovich Komkov (1926–1987) and Yevgenii Ivanovich Nefedov (1910–1976)[5] and named after geochemist Eugene Valdemar Posnjak (1888–1949).[6]
Posnjakite is an uncommon but widespread secondary mineral in the oxidised zone of copper sulfide deposits, which may be of post-mine formation. It is associated with brochantite, langite, devilline, serpierite, woodwardite, wroewolfeite, aurichalcite, azurite, malachite and chalcopyrite.[4]