2019 TEWITE

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

2020 BAJORITE

BAJORITE, Mineral of the Year 2020

We are pleased to announce that for 2020 the “Mineral of the Year” award has been assigned to Bojarite. This new mineral was found and characterized by a research team led by Nikita Chukanov (Russian Academy of Sciences, Moscow). The full description of the new mineral is available here: Chukanov, N.V., Möhn, G., Zubkova, N.V., Ksenofontov, D.A., Pekov, I.V., Agakhanov, A.A., Britvin, S.N., Desor, J. (2020): Bojarite, Cu₃(N₃C₂H₂)₃(OH)Cl₂·6H₂O, a new mineral species with a microporous metal-organic framework from the guano deposit at Pabellón de Pica, Iquique Province, Chile. Mineralogical Magazine, 84, 921-927.

Bojarite was discovered in a guano deposit on the northern slope of the Pabellón de Pica Mountain, 1.5 km south of Chanabaya village, Iquique Province, Tarapacá Region, Chile. The mineral occurs as blue fine-grained porous aggregates a few mm wide. Associated minerals are salammoniac, halite, chanabayaite, nitratine, and belloite (Fig. 1). Its ideal chemical formula is Cu₃(N₃C₂H₂)₃(OH)[Cl2(H2O)4]·2H2O, hence bojarite is a copper triazolate mineral.

Bojarite crystallizes in the cubic system, and has space group Fd 3 c, with a = 24.8047(5) Å. The crystal structure of bojarite has been refined by the Rietveld method and is definitely elegant: three Cu²⁺ cations are linked by an hydroxyl anion at the center of an equilateral triangle and are also _²⁺ connected to two nitrogen atoms of the triazole ring, leading to the formation of [Cu₃(trz)₃(OH)] building blocks [where trz = 1,2,4-triazole anion (N₃C₂H₂)–]. The third nitrogen atom of the triazole ring connects the triangular unit with adjacent units, giving rise to a three-dimensional network. The coordination of copper is completed by two longer bonds with chlorine atoms.

A fragment of the crystal structure containing the [Cu₃(trz)₃(OH)]²⁺ building block with additional Cl– anions and three additional triazole rings is shown in Fig. 2.
Bojarite is a supergene mineral formed as the result of alteration of chanabayaite in the contact zone between a deeply altered bird guano deposit and chalcopyrite-bearing amphibole gabbro.

Bojarite is the ninth new mineral found in the guano deposit at Pabellón de Pica. It is worth noting that another mineral from that same occurrence, chanabayaite, was elected as the “Mineral of the Year” in 2015.

IMA statement

IMA statement

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