Overview
"Cuprodescloizite" is a historic, now-discredited mineral name rather than a valid modern species. It was used in the nineteenth and early twentieth centuries for copper-bearing members of the descloizite family of lead vanadates. Today these materials are referred to the descloizite-mottramite series: when copper exceeds zinc the correct name is mottramite, PbCu(VO4)(OH), and when zinc dominates the name is descloizite. We include the old name here for honesty and for collectors who encounter it on antique labels, but anyone shopping for a real specimen should look for mottramite or descloizite.
Composition & structure
The descloizite-mottramite series consists of basic lead vanadates in which copper and zinc substitute for one another. Descloizite is the zinc-rich end member, PbZn(VO4)(OH), and mottramite is the copper-rich end member, PbCu(VO4)(OH); the two form a continuous solid solution. The historic term "cuprodescloizite" was applied to copper-bearing intermediate material, but because mineral names follow the dominant-element rule, such material is properly named for whichever of copper or zinc prevails. Both end members are orthorhombic and belong to the adelite-descloizite group of arsenate-vanadate minerals.
| Formula | Historic name; refers to mottramite PbCu(VO4)(OH) - descloizite PbZn(VO4)(OH) series |
| Crystal system | Orthorhombic |
| Mohs hardness | 3 to 3.5 |
| Lustre | Greasy to resinous, subadamantine |
| Colour | Green to olive, brown, or red-brown (depending on Cu/Zn) |
| Type locality | Not applicable (discredited name); mottramite type locality is Cheshire, England |
Formation & occurrence
The minerals once labelled cuprodescloizite form in the oxidised zones of lead-, zinc- and copper-bearing ore deposits. Vanadium released by weathering combines with lead and either copper or zinc to produce these secondary vanadates, typically as crusts, botryoidal coatings and small crystals on gossan and altered ore. The copper-rich (mottramite) varieties tend toward green and olive colours, while zinc-rich (descloizite) material is browner and redder. They are classic products of arid-climate oxidation zones.
Identification & similar species
Because "cuprodescloizite" spans a solid-solution series, identification really means deciding where a specimen falls between descloizite and mottramite, which usually requires chemical analysis. In hand specimen the green to olive, brown or red-brown colours, greasy to subadamantine lustre, high density and association with oxidised lead-zinc-copper ores are characteristic. Similar species include duftite, with which mottramite forms a series, and other secondary lead vanadates such as vanadinite, from which it differs in habit and chemistry.
Notable localities & collecting
The most celebrated specimens of this material come from the great oxidised orebody at Tsumeb in Namibia, a source of superb mottramite, as well as oxidised lead-zinc deposits in the southwestern United States and elsewhere. Collectors should be aware that a label reading "cuprodescloizite" is a sign of an old or imprecise determination; the specimen is almost certainly mottramite or a copper-rich descloizite. Buying under the current names ensures accuracy, and an analytically confirmed Cu/Zn ratio is the gold standard for series members.