TEWITE, Mineral of the Year 2019

We are pleased to announce that for 2019 the “Mineral of the Year” award has been assigned to tewite.

This mineral was discovered in the vicinity of Nanyang village, Huaping County, located in the south of the Panzhihua–Xichang region, southwestern China. It occurs in the Neoproterozoic Sinian light-weathered biotite–quartz monzonite, near the contact zone with gabbro. The associated minerals are alkali feldspar, biotite, clinoamphibole, ilmenite, zircon, zoisite, tourmaline, monazite-(Ce), allanite-(Ce), scheelite, tellurite and the new mineral wumuite (KAl_0.33W_2.67O₉, IMA2017-067a), in addition to an unidentified, potentially new mineral corresponding to WO₃. 

Tewite forms platy crystals that range from 0.08×0.1×0.1 to 0.1×0.2×0.5 mm in size. The crystals are greenish yellow, with a light-yellow to white streak, translucent to transparent, and with adamantine luster. Mohs hardness is 3½–4, and the tenacity is brittle. Tewite has perfect {100}, {001}, and {010} cleavages. The empirical formula, based on 19 O, is (K_1.61Na_0.06□_0.33)_∑2.00(Te_1.06W_0.35□_0.59)_∑2.00W₅O₁₉. Already first studies showed tewite to be a new mineral with a new crystal-structure type and a composition containing Te, W and K. No similar minerals or synthetic compounds corresponding to this mineral have been previously found.

Tewite has a new tungsten-bronze (TB)-type derivative structure. Distorted TeO6 octahedra break TB slabs into ribbons which are displaced by ½ a relative to their neighbors, while K partly occupies two mutually exclusive sites in hexagonal channels || c. Short-range order and displacement of K ions are likely responsible for an observed incommensurate modulation of the average structure indicated by weak satellite reflections along c*, which were not considered in the structure refinement. 

The two closest runners-up were Rudabanyaite, a new mineral with a [Ag₂Hg₂]⁴⁺ cluster cation from the Rudabánya ore deposit (Hungary) described by Herta Effenberger and co-authors (2019) in the European Journal of Mineralogy and Davidbrownite-(NH₄), a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA, described by Anthony R. Kampf and co-authors in the Mineralogical Magazine (2019).We would like to congratulate Guowu Li and co-authors on the discovery of tewite and encourage all colleagues to read about this fantastic find in the European Journal of Mineralogy article.

Li, Guowu, Xue, Yuan, Xiong, Ming (2019): Tewite: A K–Te–W new mineral species with a modified tungsten-bronze type structure, from the Panzhihua-Xichang region, southwest China. European Journal of Mineralogy 31 (1):145–152. 
https://doi.org/10.1127/ejm/2019/0031-2813

Effenberger, H., Szakáll, S., Fehér, B., Váczi, T.; Zajzon, N. (2019): Rudabányaite, a new mineral with a [Ag₂Hg₂]⁴⁺ cluster cation from the Rudabánya ore deposit (Hungary). 
European Journal of Mineralogy 31 (3):537–547.
https://doi.org/10.1127/ejm/2019/0031-2830

Kampf, A.R., Cooper, M.A., Rossman, G.R., Nash, B.P., Hawthorne, F.C., Marty, J. (2019): Davidbrownite-(NH₄), (NH₄,K)₅(V⁴⁺O)₂(C₂O₄)[PO_2.75(OH)_1.25]₄·3H₂O, a new phosphate–oxalate mineral from the Rowley mine, Arizona, USA. Mineralogical Magazine 83 (6):869-877. 
https://doi.org/10.1180/mgm.2019.56