Title
karlseifertite
Composition
Pb(Ga2Ge)(AsO4)2(OH)6
Crystal System
Trigonal
Status at Tsumeb
Confirmed
Abundance
Extremely rare
Distribution
Second oxidation zone (?)
Paragenesis
Supergene
Type Locality
Yes
Entry Type
Species TSNB386
Type Mineralogy
Joy Désor (of Mineralanalytik) and dealer Armin Schöler purchased the mineral collection of Karl Markus Seifert (1911-2000), a mining engineer who worked extensively in Namibia for many years and for the Tsumeb Corporation Limited between 1963 and 1967. A secondary phase on a specimen of germanite-bearing ore collected by Seifert was found to have a previously undescribed composition. It was subsequently approved as a new mineral, IMA 2024-007, and named karlseifertite in honour of its collector and former owner (Kampf et al. 2024a,b). Karlseifertite is a member of the dussertite group of minerals in the alunite supergroup. Type material is conserved at the Natural History Museum of Los Angeles County, California (catalogue numbers 76334 (holotype) and 76335 (co-type)).
General Notes
Karlseifertite forms rosettes of thin hexagonal plates (to 0.2 mm in diameter). It is yellow to yellow-green in colour, transparent, with a sub-adamantine lustre. It occurs on partings in germanite-chalcocite ore, sometimes accompanied by siderite (Kampf et al. 2024b; Joy Désor, pers. comm. to M. Southwood, September 2024). The germanite-rich sulphide matrix and the early 1960s collection date indicate that the type material is almost certainly from the second oxidation zone.
The crystal chemistry of karlseifertite is unusual. Kampf et al. (2024) noted that karlseifertite is the first member of the alunite supergroup containing essential germanium. Furthermore, it is the first member of the dussertite group with valency-imposed double site occupancy in one of the cation sites. Kampf et al. (2024b) give the following empirical formula for the holotype:
Pb2+0.99(Ga3+1.60Ge4+0.68Fe3+0.57Al3+0.12)∑2.97[(As5+0.67S6+0.15W6+0.09)1.00O4]2 (OH 0.99)6
The presence of tungsten in the empirical formula is also of interest.
Kampf et al. (2024b) further noted that karlseifertite is closely related to galloplumbogummite (a phosphate of Pb, Ga and Ge) and that it is close to being a Ga analogue of segnitite. (Note that an unnamed Ga analogue of segnitite was reported by Jambor et al. (1996) in the type assemblage for gallobeudantite).
Associated Minerals
chalcocite; germanite; siderite
