IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) Newsletter 42: New minerals and nomenclature modifications approved in 2018

IMA No. 2017-094

Ammoniolasalite

(NH₄)₂Mg₂(H₂O)₂₀] [V₁₀O₂₈]

Burro mine, Slick Rock district, San Miguel Co., Colorado, USA (38°2′42″N, 108°53′23″W)

Anthony R. Kampf*, Barbara P. Nash, Paul M. Adams, Joe Marty and John M. Hughes

*E-mail: akampf@nhm.org

The ammonium analogue of lasalite

Monoclinic: C2/c; structure determined

a = 24.478(3), b = 10.9413(4), c = 17.551(1) Å, β = 119.257(7)°

10.64(24), 9.43(100), 8.57(21), 7.62(26), 6.80(32), 2.891(13), 2.725(23), 2.125(13)

Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue numbers 67477, 67478, 67479, 67480 and 67481

How to cite: Kampf, A.R., Nash, B.P., Adams, P.M., Marty, J. and Hughes, J.M. (2018) Ammoniolasalite, IMA 2017-094. CNMNC Newsletter No. 42, April 2018, page 403; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-099

Ferrierite-NH₄

(NH₄,Mg_0.5)₅(Al₅Si₃₁O₇₂) · 22H₂O

Libous lignite quarry, near Chomutov, Ústí Region, Bohemia, Czech Republic

Nikita V. Chukanov*, Igor V. Pekov, Dmitriy I. Belakovskiy and Sergey N. Britvin

*E-mail: nikchukanov@yandex.ru

Zeolite supergroup

Orthorhombic: Immm

a = 19.10(1), b = 14.15(1), c = 7.489(3) Å

9.52(97), 6.95(28), 6.60(19), 3.988(61), 3.784(19), 3.547(73), 3.482(100), 3.143(37)

Type material is deposited in the collections of the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5120/1

How to cite: Chukanov, N.V., Pekov, I.V., Belakovskiy, D.I. and Britvin, S.N. (2018) Ferrierite-NH₄, IMA 2017-099. CNMNC Newsletter No. 42, April 2018, page 404; European Journalof Mineralogy, 30, 403–408.

IMA No. 2017-100

Nollmotzite

Mg[U⁵⁺(U⁶⁺O₂)₂O₄F₃] · 4H₂O

Clara mine, Black Forest Mountains, Baden-Württemberg, Germany (48°22′59″N, 8°14′47″E)

Jakub Plášil*, Anthony R. Kampf, Radek Škoda and Jiří Čejka

*E-mail: plasil@fzu.cz

New structure type

Monoclinic: Cm; structure determined

a = 7.1122(4), b = 11.7733(7), c = 8.2075(4) Å, β = 98.623(4)°

8.10(100), 4.060(31), 3.518(30), 3.420(54), 3.237(22), 3.083(26), 2.710(17), 2.015(32)

Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue numbers 66647, 66648 and 66649

How to cite: Plášil, J., Kampf, A.R., Škoda, R. and Čejka, J. (2018) Nollmotzite, IMA 2017-100. CNMNC Newsletter No. 42, April 2018, page 404; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-101

Dellagiustaite

V²⁺Al₂O₄

Sierra de Comechingones, San Luis, Argentina

Fernando Cámara*, Renato Pagano, Adriana Pagano and Luca Bindi

*E-mail: fernando.camara@unimi.it

Spinel supergroup

Cubic: Fd$3¯$m; structure determined

a = 8.1950(1) Å

2.469(19), 2.047(58), 1.576(38), 1.447(100), 1.182(27), 1.023(87), 0.915(21), 0.836(35)

Type material is deposited in the mineralogical collections of the Museo delle Collezioni di Mineralogia, Gemmologia, Petrologia e Giacimentologia, Dipartimento di Scienze della Terra “A. Desio”, Università di Milano, catalogue number MCMGPG-H2017-001

How to cite: Cámara, F., Pagano, R., Pagano, A. and Bindi, L. (2018) Dellagiustaite, IMA 2017-101. CNMNC Newsletter No. 42, April 2018, page 404; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-102

Potassic-richterite

K(NaCa)Mg₅Si₈O₂₂(OH)₂

Stora Pajsberg mine, Filipstad, Värmland, Sweden (59°47.04′N, 14°19.03′E); or Harstigen mine, Filipstad, Värmland, Sweden (59°47.10′N, 14°18.84′E)

Dan Holtstam*, Fernando Cámara, Henrik Skogby and Andreas Karlsson

*E-mail: ##Email##dan.holtstam@nrm.se##Email##

Amphibole supergroup

Monoclinic: C2/m; structure determined

a = 9.9977(3), b = 18.0409(4), c = 5.2794(2) Å, β = 104.465(4)°

8.55(36), 3.303(56), 3.181(100), 2.847(50), 2.714(37), 2.173(25), 1.668(27), 1.456(32)

Type material is deposited in the mineralogical collections of the Department of Geosciences, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden, collection number NRM19311387

How to cite: Holtstam, D., Cámara, F., Skogby, H. and Karlsson, A. (2018) Potassic-richterite, IMA 2017-102. CNMNC Newsletter No. 42, April 2018, page 404; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-103

Magnesiofluckite

CaMg(AsO₃OH)₂(H₂O)₂

Torrecillas mine, Salar Grande, Iquique Province, Tarapacá Region, Chile (20°58′13″S, 70°8′17″W)

Anthony R. Kampf*, Barbara P. Nash, Maurizio Dini and Arturo A. Molina Donoso

*E-mail: akampf@nhm.org

The Mg analogue of fluckite

Triclinic: P$1¯$⁠; structure determined

a = 8.4143(6), b = 7.5321(5), c = 6.8917(4) Å, α = 82.477(6), β = 97.682(6), γ = 95.379(6)°

7.46(78), 4.92(43), 4.191(45), 3.511(100), 3.248(81), 2.953(62), 2.796(51), 2.679(75)

Type material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue number 67257

How to cite: Kampf, A.R., Nash, B.P., Dini, M. and Molina Donoso, A.A. (2018) Magnesiofluckite, IMA 2017-103. CNMNC Newsletter No. 42, April 2018, page 404; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-084

Lasnierite

(Ca,Sr)(Mg,Fe²⁺)₂Al(P[O,F]₄)₃

Mount Ibity, ca. 30 km NNE of Soavina, Ambatofinandrahana district, and 10 km SW of Manandona, Antsirabé 2 District, Vakinankaratra Region, Antananarivo Province, Madagascar

Benjamin Rondeau*, Bertrand Devouard, Damien Jacob, Pascal Roussel, Nicolas Stéphant, Constance Boulet, Valentin Mollé, Marianna Corre, Emmanuel Fritsch, Cristiano Ferraris and Gian Carlo Parodi

*E-mail: benjamin.rondeau@univ-nantes.fr

New structure type

Orthorhombic: Pbcn; structure determined

a = 6.2771(3), b = 17.684(3), c = 8.1631(4) Å

4.421(83), 3.802(63), 3.706(100), 3.305(99), 2.890(90), 2.781(69), 2.772(67), 2.601(97)

Type material is deposited in the mineralogical collections of the Muséum National d'Histoire Naturelle (MNHN), 61 rue Buffon, 75005 Paris, France, registration number MNHN 217.001

How to cite: Rondeau, B., Devouard, B., Jacob, D., Roussel, P., Stéphant, N., Boulet, C., Mollé, V., Corre, M., Fritsch, E., Ferraris, C. and Parodi, G.C. (2018) Lasnierite, IMA 2017-084. CNMNC Newsletter No. 42, April 2018, page 405; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-104

Vandermeerscheite

4 K₂[(UO₂)₂V₂O₈] · 2H₂O

Schellkopf, Brenk, Eifel, Rhineland-Palatinate, Germany

Jakub Plášil^*, Anthony R. Kampf, Radek Škoda and Jiří Čejka

^*E-mail: ##Email##plasil@fzu.cz##Email##

Chemically close to carnotite

Monoclinic: P2₁/n; structure determined

a = 8.292(2), b = 8.251(3), c = 10.188(3) Å, β = 110.84(4)°

7.49(100), 4.147(22), 3.738(32), 3.616(20), 3.254(31), 3.132(21), 2.989(41), 2.091(13)

Cotype material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue numbers 67260, 67261 and 67262

How to cite: Plášil, J., Kampf, A.R., Škoda, R. and Čejka, J. (2018) Vandermeerscheite, IMA 2017-104. CNMNC Newsletter No. 42, April 2018, page 405; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-105

Khrenovite

Na₃$Fe23+$(AsO₄)₃

Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka peninsula, Far-Eastern Region, Russia (55°41′N, 160°14′E, 1200 m asl)

Igor V. Pekov*, Natalia N. Koshlyakova, Dmitry I. Belakovskiy, Marina F. Vigasina, Natalia V. Zubkova, Atali A. Agakhanov, Sergey N. Britvin, Evgeny G. Sidorov and Dmitry Y. Pushcharovsky

*E-mail: ##Email##igorpekov@mail.ru##Email##

Alluaudite group

Monoclinic: C2/c; structure determined

a = 12.2394(7), b = 12.7967(5), c = 6.6589(4) Å, β = 112.953 (7)°

6.40(48), 5.639(48), 3.582(41), 3.198(62), 2.939(33), 2.824(60), 2.785(100), 2.612(33)

Type material is deposited in the collections of the the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5028/1

How to cite: Pekov, I.V., Koshlyakova, N.N., Belakovskiy, D.I., Vigasina, M.F., Zubkova, N.V., Agakhanov, A.A., Britvin, S.N., Sidorov, E.G. and Pushcharovsky, D.Y. (2018) Khrenovite, IMA 2017-105. CNMNC Newsletter No. 42, April 2018, page 405; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-106

Chinchorroite

Na₂Mg₅(As₂O₇)₂(AsO₃OH)₂(H₂O)₁₀

Torrecillas mine, Salar Grande, Iquique Province, Tarapacá Region, Chile (20°58′13″S, 70°8′17″W)

Anthony R. Kampf*, Barbara P. Nash, Maurizio Dini and Arturo A. Molina Donoso

*E-mail: ##Email##akampf@nhm.org##Email##

New structure type

Triclinic: P$1¯$⁠; structure determined

a = 8.7777(2), b = 8.8570(3), c = 9.7981(7) Å, α = 91.097(6), β = 110.544(8), γ = 103.167(7)°

9.10(100), 8.63(54), 5.25(32), 4.034(49), 3.521(35), 3.036(53), 2.811(42), 2.568(36)

Type material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue number 67257

How to cite: Kampf, A.R., Nash, B.P., Dini, M. and Molina Donoso, A.A. (2018) Chinchorroite, IMA 2017-106. CNMNC Newsletter No. 42, April 2018, page 405; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-107

Nöggerathite-(Ce)

(Ce,Ca)₂Zr₂(Nb,Ti)(Ti,Nb)₂Fe²⁺O₁₄

In den Dellen (Zieglowski) pumice quarry, 1.5 km NE of Mendig, Laach Lake (Laacher See) volcano, Eifel region, Rhineland-Palatinate, Germany

Nikita V. Chukanov*, Natalia V. Zubkova, Sergey N. Britvin, Igor V. Pekov, Marina F. Vigasina, Christof Schäfer, Bernd Ternes, Willi Schüller, Vera N. Ermolaeva and Dmitry Y. Pushcharovsky

*E-mail: ##Email##chukanov@icp.ac.ru##Email##

Isostructural with zirconolite

Orthorhombic: Cmca; structure determined

a = 7.2985(3), b = 14.1454(4), c = 10.1607(4) Å

3.689(10), 2.963(91), 2.903(100), 2.540(39), 1.823(15), 1.796(51), 1.543(20), 1.519(16)

Type material is deposited in the collections of the the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5123/1

How to cite: Chukanov, N.V., Zubkova, N.V., Britvin, S.N., Pekov, I.V., Vigasina, M.F., Schäfer, C., Ternes, B., Schüller, W., Ermolaeva, V.N. and Pushcharovsky, D.Y. (2018) Nöggerathite-(Ce), IMA 2017-107. CNMNC Newsletter No. 42, April 2018, page 406; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-108

Rhabdoborite-(V)

Mg₁₂(V⁵⁺,Mo⁶⁺,W⁶⁺)_1.5O₆{[BO₃]_6-x[(P,As)O₄]_xF_2-x} (x < 1)

Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka peninsula, Far-Eastern Region, Russia (55°41′N, 160°14′E, 1200 m asl)

Igor V. Pekov*, Natalia V. Zubkova, Natalia N. Koshlyakova, Dmitry I. Belakovskiy, Marina F. Vigasina, Atali A. Agakhanov, Sergey N. Britvin, Evgeny G. Sidorov and Dmitry Y. Pushcharovsky

*E-mail: igorpekov@mail.ru

Isostructural with rhabdoborite-(W) (IMA No. 2017-109)

Hexagonal: P6₃; structure determined

a = 10.6314(4), c = 4.5661(2) Å

9.17(100), 5.301(44), 3.472(76), 2.763(64), 2.547(61), 2.226(79), 1.701(63), 1.474(31)

Type material is deposited in the collections of the the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5125/1

How to cite: Pekov, I.V., Zubkova, N.V., Koshlyakova, N.N., Belakovskiy, D.I., Vigasina, M.F., Agakhanov, A.A., Britvin, S.N., Sidorov, E.G. and Pushcharovsky, D.Y. (2018) Rhabdoborite-(V), IMA 2017-108. CNMNC Newsletter No. 42, April 2018, page 406; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-109

Rhabdoborite-(W)

Mg₁₂(W⁶⁺,V⁵⁺)_1.5O₆{[BO₃]_6-x[(P,As)O₄]_xF_2-x} (x < 1)

Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka peninsula, Far-Eastern Region, Russia (55°41′N, 160°14′E, 1200 m asl)

Igor V. Pekov*, Natalia V. Zubkova, Natalia N. Koshlyakova, Dmitry I. Belakovskiy, Marina F. Vigasina, Atali A. Agakhanov, Sergey N. Britvin, Evgeny G. Sidorov and Dmitry Y. Pushcharovsky

*E-mail: ##Email##igorpekov@mail.ru##Email##

Isostructural with rhabdoborite-(V) (IMA No. 2017-108)

Hexagonal: P6₃; structure determined

a = 10.6366(5), c = 4.5701(3) Å

9.18(100), 5.304(38), 4.595(25), 3.479(61), 2.766(29), 2.550(30), 2.228(35), 1.703(25)

Type material is deposited in the collections of the the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5126/1

How to cite: Pekov, I.V., Zubkova, N.V., Koshlyakova, N.N., Belakovskiy, D.I., Vigasina, M.F., Agakhanov, A.A., Britvin, S.N., Sidorov, E.G. and Pushcharovsky, D.Y. (2018) Rhabdoborite-(W), IMA 2017-109. CNMNC Newsletter No. 42, April 2018, page 406; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-110

Pararaisaite

CuMg[Te⁶⁺O₄(OH)₂] · 6H₂O

North Star mine, Mammoth, Tintic district, Juab Co., Utah, USA (39°55′14″N, 112°6′28″W)

Anthony R. Kampf*, Robert M. Housley and George R. Rossman

*E-mail: ##Email##akampf@nhm.org##Email##

dimorph of raisaite

Monoclinic: P2₁/c; structure determined

a = 9.6838(5), b = 5.7517(2), c = 17.634(1) Å, β = 90.553(6)°

8.77(100), 4.824(71), 4.392(43), 4.248(85), 2.733(39), 2.419(50), 1.893(48), 1.753(29)

Type material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue number 67272

How to cite: Kampf, A.R., Housley, R.M. and Rossman, G.R. (2018) Pararaisaite, IMA 2017-110. CNMNC Newsletter No. 42, April 2018, page 406; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-111

Thalhammerite

Pd₉Ag₂Bi₂S₄

Komsomolsky mine, Talnakh deposit, Noril'sk region, Russia (69°30′20″N, 88°27′17″E)

Anna Vymazalová*, František Laufek, Sergei F. Sluzhenikin, Vladimir V. Kozlov, Chris J. Stanley, Jakub Plášil, Federica Zaccarini, Giorgio Garuti and Ronald Bakker

*E-mail: anna.vymazalova@geology.cz

Known synthetic analogue

Tetragonal: I4/mmm; structure determined

a = 8.0266(2), c = 9.1531(2) Å

3.343(24), 2.839(46), 2.412(100), 2.324(61), 2.287(48), 2.220(29), 2.007(40), 1.508(30)

Type material is deposited in the mineralogical collections of the Natural History Museum, Cromwell Road, SW7 5BD London, U.K., catalogue No. BM2017,16

How to cite: Vymazalová, A., Laufek, F., Sluzhenikin, S.F., Kozlov, V.V., Stanley, C.J., Plášil, J., Zaccarini, F., Garuti, G. and Bakker, R. (2018) Thalhammerite, IMA 2017-111. CNMNC Newsletter No. 42, April 2018, page 406; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-112

Mitrofanovite

Pt₃Te₄

East Chuarvy, Fedorovo-Pana intrusion, Kola Peninsula, Russia (67°24′30″N, 36°03′00″E)

Viktor V. Subbotin, Anna Vymazalová*, František Laufek, Yevgeny E. Savchenko, Chris J. Stanley, Dmitriy A. Gabov and Jakub Plášil

*E-mail: anna.vymazalova@geology.cz

Structurally and chemically related to moncheite

Trigonal: R$3¯$m; structure determined

a = 3.9875(1), c = 35.362(7) Å

11.79(23), 5.891(100), 3.928(11), 2.851(26), 2.137(16), 2.039(18), 1.574(24), 1.310(21)

Type material is deposited in the collections of the the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 5141/1

How to cite: Subbotin, V.V., Vymazalová, A., Laufek, F., Savchenko, Y.E., Stanley, C.J., Gabov, D.A. and Plášil, J. (2018) Mitrofanovite, IMA 2017-112. CNMNC Newsletter No. 42, April 2018, page 407; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-113

Jahnsite-(MnMnZn)

Mn²⁺Mn²⁺Zn₂$Fe23+$(PO₄)₄(OH)₂· 8H₂O

Herdade dos Pendões mine, ca. 5 km N of the village of Odemira, Beja district, Portugal (37°38′33″N, 8°37′52″W)

Anthony R. Kampf*, Pedro Alves, Anatoly Kasatkin and Radek Škoda

*E-mail: akampf@nhm.org

Jahnsite group

Monoclinic: P2/a

a = 15.222(6), b = 7.187(6), c = 10.028(5) Å, β = 111.746(16)°

9.25(63), 5.00(40), 4.648(33), 3.509(41), 2.842(100),1.998(37), 1.951(30), 1.585(33)

Type material is deposited in the mineralogical collections of the Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, California, USA, catalogue number 67277

How to cite: Kampf, A.R., Alves, P., Kasatkin, A. and Škoda, R. (2018) Jahnsite-(MnMnZn), IMA 2017-113. CNMNC Newsletter No. 42, April 2018, page 407; European Journal of Mineralogy, 30, 403–408.

IMA No. 2017-078a

Kaitianite

$Ti23+$Ti⁴⁺O₅

Allende CV3 meteorite, fell at Pueblito de Allende, Chihuahua, Mexico

Ma, C.*

*E-mail: chi@gps.caltech.edu

The Ti analogue of oxyvanite

Monoclinic: C2/c

a = 10.115, b = 5.074, c = 7.182 Å, β = 112.0°

4.689(53), 3.377(75), 2.931(73), 2.662(100), 2.466(59), 1.737(66), 1.671(67), 1.451(52)

Type material is deposited in the mineralogical collections of the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA, section UNSM 3510-5

How to cite: Ma, C. (2017) Kaitianite, IMA 2017-078. CNMNC Newsletter No. 42, April 2018, page 407; European Journal of Mineralogy, 30, 403–408.

Proposal 17-H on the classification of the spinel supergroup is accepted. The fifty-three minerals of the spinel supergroup are divided into three groups on the basis of dominant X anion: O^2– (oxyspinel), S^2– (thiospinel), and Se^2– (seleniospinel). Each group is divided into subgroups according to the dominant valence and then the dominant constituent (or heterovalent-pair of constituents) represented by the letter B in the formula AB₂X₄. The oxyspinel group can be divided into spinel subgroup 2-3 (A²⁺$B23+$O₄) and ulvöspinel subgroup 4-2 (A⁴⁺$B23+$O₄), thiospinel group into carrollite subgroup 1-3.5 (A¹⁺$B23.5+$S₄) and linnaeite subgroup 2-3 (A²⁺$B23+$S₄), and the selenospinel group into bornhardtite subgroup 2-3 (A²⁺$B23+$Se₄) and tyrrellite. Once the subgroup is established by the valence of B and the dominant B-cation, then the mineral species is identified by the dominant A-cation. There are thirty species in the oxyspinel group, twenty in the thiospinel group and three in the seleniospinel group.

Proposal 17-I is accepted. A re-evaluation of the site occupancies in flurlite, using BVS calculations, resulted in a change in the dominant cation in the M1 site from Mn²⁺ to Zn. Consequently, the end-member formula for flurlite becomes ^[5]Zn^[6]Zn₃^[6]Fe³⁺(PO₄)₃(OH)₂(H₂O)₇· 2H₂O.

Proposal 18-A is accepted, and the formula for eztlite is redefined, according to new analytical results. The previously accepted formula, published by Sidney Williams in 1982, was $Fe63+Pb22+$(Te⁴⁺O₃)₃(Te⁶⁺O₆)(OH)₁₀· nH₂O, with n ≈ 8. This formula is now redefined to $Pb22+Fe33+$(Te⁴⁺O₃)₃(SO₄)O₂Cl.

In the IMA List of Minerals the ideal chemical formulae of kalsilite and nepheline are given as KAlSiO₄ and NaAlSiO₄, respectively. Whereas the formula of kalsilite is correct, nepheline must contain some amount of potassium substituting for sodium. Both kalsilite and nepheline are hexagonal, space group P6₃. In kalsilite, which has a smaller unit cell, all cavities which host alkali cations have a hexagonal outline and are occupied by potassium; in nepheline, due to the doubling of the a parameter, there are 3 cavities with oval outline and 1 cavity with hexagonal outline: the former are occupied by sodium, the latter by potassium. Accordingly, the chemical formula of nepheline should be Na₃K(Al₄Si₄O₁₆). All known chemical analyses of nepheline, including those of nepheline from the type locality (Monte Somma − Vesuvius area, Italy) match the above formula. Therefore potassium is an essential constituent of nepheline and it should appear in the chemical formula of the mineral. This is an executive decision taken by the officers of the IMA CNMNC.