Articles | Volume 34, issue 1
Eur. J. Mineral., 34, 143–148, 2022
https://doi.org/10.5194/ejm-34-143-2022
Eur. J. Mineral., 34, 143–148, 2022
https://doi.org/10.5194/ejm-34-143-2022

CNMNC Newsletter 24 Feb 2022

CNMNC Newsletter | 24 Feb 2022

IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 65

IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 65
Ritsuro Miyawaki1, Frédéric Hatert2, Marco Pasero3, and Stuart J. Mills4 Ritsuro Miyawaki et al.
  • 1Chairman, CNMNC | Department of Geology, National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba 305-0005, Japan
  • 2Vice-Chairman, CNMNC | Laboratoire de Minéralogie, Université de Liège, Bâtiment B18, Sart Tilman, 4000 Liège, Belgium
  • 3Vice-Chairman, CNMNC | Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56126 Pisa, Italy
  • 4Secretary, CNMNC | Geosciences, Museum Victoria, P.O. Box 666, Melbourne, Victoria 3001, Australia

Correspondence: Marco Pasero (marco.pasero@unipi.it)

The information given here is provided by the IMA Commission on New Minerals, Nomenclature and Classification for comparative purposes and as a service to mineralogists working on new species.

Each mineral is described in the following format:

  • mineral name, if the authors agree on its release prior to the full description appearing in press;

  • chemical formula (ideal formula);

  • mineral symbol;

  • type locality;

  • full authorship of proposal;

  • e-mail address of corresponding author;

  • relationship to other minerals;

  • crystal system, space group, structure determined, yes or no;

  • unit-cell parameters;

  • strongest lines in the X-ray powder diffraction pattern;

  • type specimen repository and specimen number;

  • citation details for the mineral prior to publication of full description.

Citation details concern the fact that this information will be published in the European Journal of Mineralogy on a routine basis, as well as being added month by month to the commission's website. It is still a requirement for the authors to publish a full description of the new mineral.

No other information will be released by the commission.

1 New mineral proposals approved in December 2021

IMA no. 2021-062a

  • Slyudyankaite

  • Sdy

  • Na28Ca4(Si24Al24O96)(SO4)6(S6)1/3(CO2)2H2O

  • Malo-Bystrinskoe deposit, Baikal Lake area, eastern Siberia, Russia (514050′′ N, 1032518′′ E)

  • Anatoly N. Sapozhnikov, Nadezhda B. Bolotina, Nikita V. Chukanov*, Ekaterina V. Kaneva, Roman Y. Shendrik, Marina F. Vigasina, and Larisa A. Ivanova

  • *E-mail: nikchukanov@yandex.ru

  • Sodalite group

  • Triclinic: P1; structure determined

  • a= 9.0523(4), b= 12.8806(6), c= 25.681(1) Å, α= 89.988(2), β= 90.052(1), γ= 90.221(1)

  • 12.93(6), 6.45(20), 3.716(100), 2.878(12), 2.625(23), 2.431(6), 2.143(11), 1.784(9)

  • Type material is deposited in the collections of the Sidorov Mineralogical Museum (INRTU), Lermontova St. 83, Irkutsk 664074, Russia, registration numbers MMU/MF 27296 (holotype) and MMU/MF 27297 (cotype)

  • How to cite: Sapozhnikov, A. N., Bolotina, N. B., Chukanov, N. V., Kaneva, E. V., Shendrik, R. Y., Vigasina, M. F., and Ivanova, L. A.: Slyudyankaite, IMA 2021-062a, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-081

  • Kozłowskiite

  • Kzw

  • Ca4Fe2+Sn3(Si2O7)2(Si2O6OH)2

  • In a pegmatite of the Karkonosze granite, Szklarska Poręba Huta quarry, Lower Silesia, Poland (504940′′ N, 152922′′ E)

  • Adam Pieczka*, Sylwia Zelek-Pogudz, Bożena Gołębiowska, Katarzyna M. Stadnicka, and R. James Evans

  • *E-mail: pieczka@agh.edu.pl

  • Kristiansenite group

  • Triclinic (pseudomonoclinic): C1; structure determined

  • a= 10.0170(3), b= 8.3860(2), c= 13.3421(4) Å, α= 90, β= 109.050(3), γ= 90

  • 5.190(73), 4.569(30), 3.906(19), 3.153(65), 3.094(28), 3.089(100), 2.595(27), 2.141(31)

  • Type material is deposited in the collections of the Mineralogical Museum, University of Wrocław, Cybulskiego 30, 50–205 Wrocław, Poland, catalogue number MMWr IV7929

  • How to cite: Pieczka, A., Zelek-Pogudz, S., Gołębiowska, B., Stadnicka, K. M., and Evans, R. J.: Kozłowskiite, IMA 2021-081, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-082

  • Medvedevite

  • Mvv

  • KMn2+V2O6Cl2H2O

  • Toludskoe lava field, 2012–2013 Tolbachik Fissure Eruption, Plosky Tolbachik volcano, Kamchatka, Russia (554502′′ N, 1601941′′ E)

  • Andrey P. Shablinskii*, Margarita S. Avdontseva, Lidiya P. Vergasova, Stanislav K. Filatov, Evgenia Y. Avdontseva, Alexey V. Povolotskiy, Svetlana V. Moskaleva, Anatoly A. Kargopoltsev, and Sergey N. Britvin

  • *E-mail: shablinskii.andrey@mail.ru

  • New structure type

  • Monoclinic: P21/c; structure determined

  • a= 7.1863(2), b= 10.1147(3), c= 12.7252(4) Å, β= 106.243(3)

  • 7.79(100), 5.70(11), 4.75(14), 3.89(29), 3.25(53), 3.05(19), 2.958(79), 2.850(33)

  • Type material is deposited in the collections of the Saint Petersburg State University mineralogical museum, University Emb. 7/9, St. Petersburg 199034, Russia, catalogue number 1/19900

  • How to cite: Shablinskii, A. P., Avdontseva, M. S., Vergasova, L. P., Filatov, S. K., Avdontseva, E. Y., Povolotskiy, A. V., Moskaleva, S. V., Kargopoltsev, A. A., and Britvin, S. N.: Medvedevite, IMA 2021-082, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-083

  • Tennantite-(Cd)

  • Tnt-Cd

  • Cu6(Cu4Cd2)As4S13

  • Berenguela mining district, Pacajes Province, La Paz, Bolivia

  • Cristian Biagioni*, Anatoly V. Kasatkin, Jiří Sejkora, Fabrizio Nestola, and Radek Škoda

  • *E-mail: cristian.biagioni@unipi.it

  • Tetrahedrite group

  • Cubic: I43m; structure determined

  • a= 10.3088(2) Å

  • 4.206(7), 2.973(100), 2.574(12), 2.428(4), 2.019(3), 1.881(5), 1.821(27), 1.553(8)

  • Type material is deposited in the collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskiy Prospekt 18–2, Moscow 119071, Russia, registration number 5755/1 (holotype), and the Department of Mineralogy and Petrology, National Museum of Prague, Cirkusová 1740, 19300 Prague 9, Czech Republic, registration number P1P 47/2021 (cotype)

  • How to cite: Biagioni, C., Kasatkin, A. V., Sejkora, J., Nestola, F., and Škoda, R.: Tennantite-(Cd), IMA 2021-083, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-084

  • Höslite

  • Hös

  • Fe33+(VO4)2(SO4)(OH)(H2O)43H2O

  • Struhadlo deposit, near the Struhadlo village, 10 km west of Klatovy, Plzeň region, Southern Bohemia, Czech Republic (492351.11′′ N, 131120.61′′ E)

  • Pavel Škácha*, Jiří Sejkora, Gwladys Steciuk, Jakub Plášil, and Radek Škoda

  • *E-mail: skachap@seznam.cz

  • Structurally similar to schubnelite

  • Monoclinic: P21/c; structure determined

  • a= 8.657(3), b= 10.443(4), c= 20.4996(7) Å, β= 93.32(2)

  • 10.233(100), 6.800(17), 6.422(9), 5.116(10), 3.411(12), 3.233(8), 3.179(13), 3.125(9)

  • Type material is deposited in the collections of the Department of Mineralogy and Petrology, National Museum in Prague, Cirkusová 1740, 19300 Prague 9, Czech Republic, catalogue number P1P 30/2021

  • How to cite: Škácha, P., Sejkora, J., Steciuk, G., Plášil, J., and Škoda, R.: Höslite, IMA 2021-084, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-086

  • Gurzhiite

  • Grz

  • Al(UO2)(SO4)2F10H2O

  • 495 m level of the underground Mine 2, Bykogorskoe U deposit, Byk Mountain, Stavropol Krai, Northern Caucasus, Russia (441105.4′′ N, 425731.5′′ E)

  • Anatoly V. Kasatkin*, Jakub Plášil, Nikita V. Chukanov, Radek Škoda, Fabrizio Nestola, Atali A. Agakhanov, and Dmitry I. Belakovskiy

  • *E-mail: anatoly.kasatkin@gmail.com

  • A lower hydrate of straßmannite, with different structure

  • Triclinic: P1; structure determined

  • a= 7.193(2), b= 11.760(2), c= 11.792(2) Å, α= 67.20(3), β= 107.76(3), γ= 89.99(3)

  • 10.24(100), 6.76(10), 5.40(14), 5.11(54), 3.618(8), 3.405(11), 3.348(7), 3.065(11)

  • Type material is deposited in the collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskiy Prospekt 18–2, Moscow 119071, Russia, registration number 5756/1

  • How to cite: Kasatkin, A. V., Plášil, J., Chukanov, N. V., Škoda, R., Nestola, F., Agakhanov, A. A., and Belakovskiy, D. I.: Gurzhiite, IMA 2021-086, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-088

  • Bolotinaite

  • Bltn

  • (Na7□)(Al6Si6O24)F4H2O

  • In den Dellen (Zieglowski) pumice quarry, 1.5 km northeast of Mendig, Laach Lake (Laacher See) paleovolcano, Eifel region, Rhineland-Palatinate, Germany (502334′′ N, 71704′′ E)

  • Nikita V. Chukanov*, Natalia V. Zubkova, Christof Schäfer, Igor V. Pekov, Marina F. Vigasina, Dmitry I. Belakovskiy, Sergey N. Britvin, Vasiliy O. Yapaskurt, and Dmitry Y. Pushcharovsky

  • *E-mail: nikchukanov@yandex.ru

  • Sodalite group

  • Cubic: I43m; structure determined

  • a= 9.0228(1) Å

  • 6.36(47), 4.502(10), 3.679(100), 2.851(28), 2.603(29), 2.126(18), 1.770(7), 1.595(7)

  • Type material is deposited in the collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskiy Prospekt 18–2, Moscow 119071, Russia, registration number 5754/1

  • How to cite: Chukanov, N. V., Zubkova, N. V., Schäfer, C., Pekov, I. V., Vigasina, M. F., Belakovskiy, D. I., Britvin, S. N., Yapaskurt, V. O., and Pushcharovsky, D. Y.: Bolotinaite, IMA 2021-088, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-089

  • Sulfatoredmondite

  • Srdm

  • [Pb8O2Zn(OH)6](SO4)46H2O

  • Redmond mine, Haywood Co., North Carolina, USA (354049′′ N, 830107′′ W)

  • Anthony R. Kampf*, Jason B. Smith, John M. Hughes, Chi Ma, and Christopher Emproto

  • *E-mail: akampf@nhm.org

  • Structurally related to redmondite and hydroredmondite

  • Monoclinic: C2/m; structure determined

  • a= 17.294(2), b= 7.3668(9), c= 12.727(2) Å, β= 110.622(9)

  • 8.10(100), 6.23(48), 5.86(46), 3.115(78), 2.892(63), 2.779(63), 2.706(47), 1.827(46)

  • Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue numbers 76181, 76182 and 76183

  • How to cite: Kampf, A. R., Smith, J. B., Hughes, J. M., Ma, C., and Emproto, C.: Sulfatoredmondite, IMA 2021-089, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

2 New mineral proposals approved in January 2022

IMA no. 2021-090

  • Calcioancylite-(La)

  • Canc-La

  • (LaCa)(CO3)2(OH)(H2O)

  • Gejiu intrusion, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province, China (232940′′ N, 1030441′′ E)

  • Yanjuan Wang, Xiangping Gu, Guochen Dong*, Zenqian Hou, Zhusen Yang, Guang Fan, Yufei Wang, Chao Tang, Yinhang Cheng, and Kai Qu

  • *E-mail: donggc@cugb.edu.cn

  • Ancylite group

  • Orthorhombic: Pmcn; structure determined

  • a= 5.0253(3), b= 8.5152(6), c= 7.2717(6) Å

  • 4.322(75), 3.693(68), 2.956(80), 2.640(47), 2.520(55), 2.335(100), 2.077(44), 2.012(42)

  • Type material is deposited in the mineralogical collections of the Geological Museum of China, no. 16, Yangrou Hutong, Xisi, Beijing 100031, People's Republic of China, catalogue number M16129

  • How to cite: Wang, Y., Gu, X., Dong, G., Hou, Z., Yang, Z., Fan, G., Wang, Y., Tang, C., Cheng, Y., and Qu, K.: Calcioancylite-(La), IMA 2021-090, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-091

  • Cubothioplumbite

  • Ctpb

  • [Pb4(OH)4]Pb(S2O3)3

  • Redmond mine, Haywood Co., North Carolina, USA (354049′′ N, 830107′′ W)

  • Anthony R. Kampf*, Jason B. Smith, John M. Hughes, Chi Ma, and Christopher Emproto

  • *E-mail: akampf@nhm.org

  • A dimorph of hexathioplumbite (IMA no. 2021-092; this newsletter)

  • Cubic: Pa3; structure determined

  • a= 14.918(1) Å

  • 5.28(56), 3.732(57), 3.619(100), 3.346(64), 3.262(81), 2.490(92), 1.803(52), 1.700(49)

  • Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue numbers 76184, 76185 and 76186

  • How to cite: Kampf, A. R., Smith, J. B., Hughes, J. M., Ma, C., and Emproto, C.: Cubothioplumbite, IMA 2021-091, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-092

  • Hexathioplumbite

  • Htpb

  • [Pb4(OH)4]Pb(S2O3)3

  • Redmond mine, Haywood Co., North Carolina, USA (354049′′ N, 830107′′ W)

  • Anthony R. Kampf*, Jason B. Smith, John M. Hughes, Chi Ma, and Christopher Emproto

  • *E-mail: akampf@nhm.org

  • A dimorph of cubothioplumbite (IMA no. 2021-091; this newsletter)

  • Hexagonal: P63; structure determined

  • a= 10.721(1), c= 8.6541(6) Å

  • 6.32(67), 3.511(100), 3.359(70), 3.249(86), 2.733(77), 2.536(89), 2.476(43), 1.837(52)

  • Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA, catalogue numbers 76187, 76188 and 76189

  • How to cite: Kampf, A. R., Smith, J. B., Hughes, J. M., Ma, C., and Emproto, C.: Hexathioplumbite, IMA 2021-092, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-094

  • Ferrofettelite

  • Fftt

  • [Ag6As2S7][Ag10FeAs2S8]

  • Glasberg quarry, Nieder-Beerbach, Odenwald, Germany (494749′′ N, 84138′′ E)

  • Luca Bindi* and Robert T. Downs

  • *E-mail: luca.bindi@unifi.it

  • The Fe analogue of fettelite

  • Monoclinic: C2; structure determined

  • a= 26.011(2), b= 15.048(1), c= 15.513(1) Å, β= 90.40(1)

  • 3.18(50), 3.014(100), 3.004(60), 2.930(15), 2.755(40), 2.501(30), 2.484(20), 1.880(30)

  • Type material is deposited in the collections of the University of Arizona Gem and Mineral Museum, 115 N Church Ave., Tucson, AZ 85701, USA, catalogue number 22716

  • How to cite: Bindi, L., and Downs, R. T.: Ferrofettelite, IMA 2021-094, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-096

  • Franksousaite

  • Fns

  • PbCu(Se6+O4)(OH)2

  • El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia (194915′′ S, 655500′′ W)

  • Hexiong Yang*, James A. McGlasson, Ronald B. Gibbs, and Robert T. Downs

  • *E-mail: hyang@arizona.edu

  • The Se6+ analogue of linarite

  • Monoclinic: P21/m; structure determined

  • a= 9.8208(3), b= 5.7340(2), c= 4.7498(1) Å, β= 102.683(2)

  • 9.548(22), 4.917(24), 4.578(35), 3.602(60), 3.193(100), 3.150(50), 2.621(21), 1.828(21)

  • Type material is deposited in the collections of the University of Arizona Gem and Mineral Museum, 115 N Church Ave., Tucson, AZ 85701, USA, catalogue number 22713 (holotype), and the RRUFF Project, deposition number R210012 (cotype)

  • How to cite: Yang, H., McGlasson, J. A., Gibbs, R. B., and Downs, R. T.: Franksousaite, IMA 2021-096, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-097

  • Mariakrite

  • Mari

  • [Ca4Al2(OH)12(H2O)4][Fe2S4]

  • Ca. 2 km south-east of the Hatrurim Junction (road no. 31), Hatrurim Basin, Negev Desert, Israel

  • Michail N. Murashko, Yevgeny Vapnik, Natalia S. Vlasenko, Oleg S. Vereshchagin, Yulia S. Shelukhina, Igor V. Pekov, and Sergey N. Britvin*

  • *E-mail: sbritvin@gmail.com

  • Hydrotalcite supergroup

  • Triclinic: P1; structure determined

  • a= 5.7107(2), b= 9.9952(4), c= 10.9095(4) Å, α= 98.678(3), β= 90.100(3), γ= 90.019(3)

  • 10.83(100), 9.90(39), 5.42(75), 3.96(22), 3.523(19), 2.856(37), 2.400(23), 2.241(20)

  • Type material is deposited in the collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskiy Prospekt 18–2, Moscow 119071, Russia, registration number 5694/1

  • How to cite: Murashko, M. N., Vapnik, Y., Vlasenko, N. S., Vereshchagin, O. S., Shelukhina, Y. S., Pekov, I. V., and Britvin, S. N.: Mariakrite, IMA 2021-097, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

IMA no. 2021-098

  • Tetrahedrite-(Mn)

  • Ttr-Mn

  • Cu6(Cu4Mn2)Sb4S13

  • Teine mine, Sapporo, Hokkaido, Japan (430558′′ N, 141 1148′′ E)

  • Koichi Momma*, Masaaki Shimizu, Yoko Kusaba, and Yoshiya Ohki

  • *E-mail: k-momma@kahaku.go.jp

  • Tetrahedrite group

  • Cubic: I43m; structure determined

  • a= 10.35953(6) Å

  • 3.669(9), 2.995(100), 2.773(6), 2.593(15), 2.445(7), 1.893(6), 1.833(29), 1.563(12)

  • Type material is deposited in the mineralogical collections of the National Museum of Nature and Science, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan, specimen number MSN-M49019

  • How to cite: Momma, K., Shimizu, M., Kusaba, Y., and Ohki, Y.: Tetrahedrite-(Mn), IMA 2021-098, in: CNMNC Newsletter 65, Eur. J. Mineral., 34, https://doi.org/10.5194/ejm-34-143-2022, 2022.

3 Nomenclature/classification proposals approved in January 2022

3.1 Revised formula for lithiomarsturite, LiCaMn3Si5O14(OH)

In the IMA List of Minerals the chemical formula of lithiomarsturite is given as LiMn22+Ca2Si5O14(OH). However, a crystal structure study carried out on holotype material (Am. Mineral., 75, 409–414, 1990) clearly shows that Ca is hosted at the 7-fold coordinated M4 site (M4Ca1.00), whereas Mn is the dominant constituent at the three 6-fold coordinated sites: M1Mn1.00, M2(Mn0.77Ca0.23), and M3Mn1.00. Accordingly, the end-member formula should be written as LiCaMn3Si5O14(OH). This formula matches the formula of the related mineral marsturite, NaCaMn3Si5O14(OH). This is an executive decision taken by the officers of the IMA-CNMNC.

3.2 IMA 21-I: a proposed correction to the formula of rouvilleite

Proposal 21-I is accepted, and the formula of rouvilleite is changed from Na3CaMn2+(CO3)3F to Na3Ca2(CO3)3F.

3.3 IMA 21-J: redefinition of angastonite as an amorphous mineral

Proposal 21-J is accepted, and angastonite is redefined as an amorphous mineral species, with the ideal formula CaMgAl2(PO4)2(OH)47H2O.

3.4 IMA 21-K: grandviewite, Cu3Al2(SO4)(OH)10H2O: proposal for its redefinition

Proposal 21-K is accepted, and grandviewite is redefined as a hydrated copper–aluminum hydroxy-sulfate, having the ideal formula Cu3Al2(SO4)(OH)10H2O (Z= 2) and a triclinic symmetry, with space group P1, a= 6.002(3), b= 10.54(3), c= 11.249(8) Å, α= 72.1(2), β= 81.6(6), γ= 86.1(8).

3.5 IMA 21-L: discreditation of luinaite-(OH), (Na,□)(Fe2+,Mg)3Al6(BO3)3Si6O18(OH)4, a mineral species of the tourmaline supergroup

Proposal 21-L is accepted, and luinaite-(OH) is discredited. This monoclinic tourmaline-type species, with a simplified composition (Na,□)(Fe2+,Mg)3Al6(BO3)3Si6O18(OH)4, was approved with IMA number 2009-046. It is now considered a structurally similar polymorph of schorl, since it only differs in terms of a slight structural distortion from the typical trigonal tourmaline structure.