IMA 2016 Mineral of the Year: Merelaniite

The International Mineralogical Association is pleased to announce that the Mineral of the Year award for 2016 goes to merelaniite, Mo₄Pb₄VSbS₁₅.

This mineral was discovered in collector specimens from the Merelani region in northeastern Tanzania, and investigated by John A. Jaszczak (Michigan Technological University, Houghton, USA), Michael S. Rumsey (Natural History Museum, London, UK), Luca Bindi (Università di Firenze, Florence, Italy), Stephen A. Hackney (Michigan Technological University), Michael A. Wise (National Museum of Natural History, Washington DC, USA), Chris J. Stanley (Natural History Museum, London), and John Spratt (Natural History Museum, London).

(top) A cylindrical whisker of merelaniite (0.73 mm long) perched on green dravite; Merelani, Tanzania. (bottom) Scanning electron microscope image revealing the scroll-type structure of a 0.07 mm long segment of a merelaniite whisker.

Merelaniite, whose unusual whisker-like crystals were initially mistaken for molybdenite, is actually a new member of the cylindrite group (Jaszczak et al. 2016). The new species is remarkable not only for its morphology, which is reminiscent of slender microscopic “scrolls”, and its structure, which is composed of alternating pseudo-tetragonal (PbS-type) and pseudo-hexagonal (MoS₂-type) layers, but also for the fact that it comes from the famous mining area that has produced the gemstone tanzanite (vanadium-bearing blue zoisite) for 50 years. Other unusual minerals found in association with merelaniite are well-crystallized wurtzite and alabandite, which represent just one evolutionary stage in the complex metamorphic history of the Merelani deposits. We would like to congratulate John Jaszczak, Mike Rumsey, and their co-authors on this award and encourage all readers to learn more about merelaniite from the open-access article in Minerals (www.mdpi.com/2075-163X/6/4/115).

The close runner-ups were the Pb–Cu–Te oxysalt andychristyite (Kampf et al. 2016a), and the mineral vanarsite, which contains As–V polyanions (Kampf et al. 2016b).

References

Jaszczak JA and 6 coauthors (2016) Merelaniite, Mo4Pb4VSbS15, a new molybdenum-essential member of the cylindrite group, from the Merelani tanzanite deposit, Lelatema Mountains, Manyara Region, Tanzania. Minerals 6:115

Kampf AR, Cooper MA, Mills SJ, Housley RM, Rossman GR (2016a) Lead-tellurium oxysalts from Otto Mountain near Baker, California, USA: XII. Andychristyite, PbCu²⁺Te⁶⁺O₅(H₂O), a new mineral with hcp stair-step layers. Mineralogical Magazine 80: 1055-1065

Kampf AR, Hughes JM, Nash BP, Marty J (2016b) Vanarsite, packratite, morrisonite, and gatewayite: four new minerals containing the [As³⁺(V^4+,5+)₁₂As⁵⁺₆O₅₁] heteropolyanion, a novel polyoxometalate cluster. Canadian Mineralogist 54: 145-162