Introduction
The cerite supergroup is constituted by two groups of isostructural trigonal R3c (#161) minerals, cerite (silicates) and merrillite (phosphates). The merrillite group is subdivided into two subgroups: merrillite (without OH in the Ø site) and whitlockite (with OH in the Ø site).
A general formula for the cerite supergroup is A 9XM[TO3(Ø)]7W 3, where: A = Ce, La, Ca, Sr, (Na), (other REE); X = □ [vacancy], Ca and Na; M = Mg, Fe2+, Fe3+, Al and Mn; T = Si and P; Ø = O and OH; W = □, OH and F.
The new nomenclature has been approved by the International Mineralogical Association (IMA) Commission on New Minerals, Nomenclature and Classification (CNMNC) (Miyawaki et al., Reference Miyawaki, Hatert, Pasero and Mills2020). It is based on the dominant species of the dominant valence at each site. Table 1 gives the dominant site occupation for the cerite-supergroup minerals.
Table 1. Dominant site occupation for the cerite-supergroup minerals.
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20210113092846590-0984:S0026461X20000869:S0026461X20000869_tab1.png?pub-status=live)
Nomenclature considerations
Cerite [later renamed cerite-(Ce)] was the first mineral in the group to be described. Therefore, it gives its name to the supergroup and also to the group composed of silicates. This follows the IMA-CNMNC procedures of Mills et al. (Reference Mills, Hatert, Nickel and Ferraris2009). Cerite was first described by Cronstedt (Reference Cronstedt1751) as ‘tungsten’. It was renamed by Hisinger and Berzelius (Reference Hisinger and Berzelius1804) as cerite, after the dwarf planet Ceres discovered by the Italian astronomer Guiseppe Piazzi in 1801. They discovered and named the chemical element cerium in this mineral.
The cerite supergroup is composed of 12 valid mineral species, three of them are pre-IMA [cerite-(Ce), merrillite and whitlockite], one was described in the 20th Century (strontiowhitlockite), and all the other eight were described in the 21st century. ‘Bobdownsite’ (IMA2008-037), a purported fluorophosphate analogue of whitlockite with Ø = F, was described by Tait et al. (Reference Tait, Barkley, Thompson, Origlieri, Evans, Prewitt and Yang2011) and discredited in McCubbin et al. (Reference McCubbin, Phillips, Adcock, Tait, Steele, Vaughn, Fries, Atudorei, Vander Kaaden and Hausrath2018). Hedegaardite and keplerite have been approved (IMA2014-069, Witzke et al., Reference Witzke, Phillips, Woerner, Coutinho, Färber and Contreira Filho2015; and IMA2019-108, Britvin et al., Reference Britvin, Galuskina, Vlasenko, Vereshchagin, Bocharov, Krzhizhanovskaya, Shilovskikh, Galuskin, Vapnik and Obolonskaya2020, respectively) but their complete descriptions have not yet been published. Additionally, a possible Mn-analogue to cerite-(Ce) was reported by Holtstam et al. (Reference Holtstam, Bindi, Karlsson, Langhof, Zack, Bonazzi and Persson2020). There are a large number of synthetic compounds with the cerite structure, including arsenates and vanadates [see for instance Lipp and Schleid (Reference Lipp and Schleid2008), Deyneko et al. (Reference Deyneko, Petrova, Leonidova, Nikiforov and Lazoryak2017) and Lazoryak et al. (Reference Lazoryak, Deyneko, Aksenov, Stefanovich, Fortalnova, Petrova, Baryshnikova, Kosmyna and Shekhovtsov2018)]. This indicates that the cerite supergroup may still grow substantially. These compounds are synthesised due to their important technological properties. The vanadates are currently considered promising for white light emission diodes, phosphors and light converters (Lazoryak et al., Reference Lazoryak, Deyneko, Aksenov, Stefanovich, Fortalnova, Petrova, Baryshnikova, Kosmyna and Shekhovtsov2018).
When simplified, the crystal structure of these minerals involves three 8- and 9-fold-coordinated A sites, one six-coordinated X, one octahedral M site and three almost perfect [TO3(Ø)] tetrahedral sites. The cerite-supergroup minerals structure consists of [M(TO4)6] clusters linked by {A 9X(TO3Ø)} groups (Figs 1 and 2).
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20210113092846590-0984:S0026461X20000869:S0026461X20000869_fig1.png?pub-status=live)
Fig. 1. Schematic view of the crystal structure of cerite-supergroup minerals, drawn using VESTA 3 (Momma and Izumi, Reference Momma and Izumi2011).
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20210113092846590-0984:S0026461X20000869:S0026461X20000869_fig2.png?pub-status=live)
Fig. 2. Schematic views of the crystal structure of cerite-(Ce) and merrillite, drawn using VESTA 3 (Momma and Izumi, Reference Momma and Izumi2011).
The end-member formulas for merrillite, ferromerrillite, whitlockite and strontiowhitlockite are charge balanced. For the other eight species they are not charge balanced. Charge balance is attained by substitutions at the A, X and M sites. In these cases, it is not advisable to force the existence of a specific member formula. For example, although the taipingite-(Ce) formula could be idealised as (Ce7Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3, this is not the only mechanism by which charge balance can be obtained, and Ca is not an essential element in the species. If the minority element at site X were Sr or Ba, the species remains the same. Otherwise, there would be an unwanted proliferation of species, controlled by non-dominant elements. Possible, but unspecified, charge-balancing substituents are best indicated by ‘#’, as done in the list of species in the Appendix. This approach is also used to great effect in the pyrochlore supergroup (Atencio et al., Reference Atencio, Andrade, Christy, Gieré and Kartashov2010).
Some comments could be made on the naming of the supergroup members. As cerite-(Ce) has Mg, and cerite-(La) has Fe3+ in the M site, cerite-(La) is renamed here as ferricerite-(La). Note that inconsistent precedents for the use of chemical prefixes have been set in the whitlockite and merrillite subgroups. ‘Ferro’ in ferromerrillite refers to the composition of the M site, while ‘strontio’ of strontiowhitlockite refers to the X site. This means that ‘ferrostrontiowhitlockite’ is a hypothetical member of the group, a long and awkward name. If the prefix were restricted to refer to the M site only, then strontiowhitlockite would need to be renamed. Such prefix usage might also encourage renaming of matyhite as ‘ferrokeplerite’ and wopmayite as ‘manganowhitlockite’. However, as the renaming of well-established minerals is traumatic and should be avoided, we did not propose changes at this moment beyond that of cerite-(La) to ferricerite-(La). Other minerals with such chemical inconsistencies have also been renamed in the past (c.f. aluminopharmacosiderite to pharmacoalumite; Rumsey et al., Reference Rumsey, Mills and Sprattl2010).
Acknowledgements
DA acknowledges the Brazilian agencies FAPESP (processes 2014/50819-9 and 2019/23498-0), and CNPq (research productivity). AAA acknowledges the Brazilian agency FAPESP (processes 2015/26689-0 and 2017/25426-1). We acknowledge all members of the IMA Commission on New Minerals, Nomenclature and Classification, the Principal Editor Stuart Mills, and two anonymous reviewers for their helpful suggestions and comments.
Appendix. Cerite supergroup species
‘□’ indicates a vacancy and ‘#’ indicates possible, but unspecified, charge-balancing substituents.
Cerite-(Ce)
IMA Number: pre-IMA mineral
IMA List formula: (Ce,La,Ca)9(Mg,Fe3+)(SiO4)3(SiO3OH)4(OH)3
Generalised formula: (Ce,#)9(□,#)(Mg,#)(SiO4)3[SiO3(OH)]4(OH)3
Original description: Hisinger and Berzelius (Reference Hisinger and Berzelius1804)
Type locality: St Görans Mine, Bastnäs Mines, Riddarhyttan, Skinnskatteberg, Västmanland County, Sweden
Crystal structure: Moore and Shen (Reference Moore and Shen1983)
Unit-cell parameters: a = 10.779(6) Å, c = 38.0610(70) Å and V = 3829.73 Å3
Ferricerite-(La)
[Originally named cerite-(La)]
IMA Number: 2001-042
IMA List formula: (La,Ce,Ca)9(Fe3+,Ca,Mg)(SiO4)3(SiO3OH)4(OH)3
Generalised formula: (La,#)9(□,#)(Fe3+,#)(SiO4)3[SiO3(OH)]4(OH)3
Original description: Pakhomovsky et al. (Reference Pakhomovsky, Men'Shikov, Yakovenchuk, Ivanyuk, Krivovichev and Burns2002)
Type localities: Yukspor Mt, Khibiny Massif, Murmansk Oblast, Russia
Crystal structure: Pakhomovsky et al. (Reference Pakhomovsky, Men'Shikov, Yakovenchuk, Ivanyuk, Krivovichev and Burns2002)
Unit-cell parameters: a = 10.7493(6) Å, c = 38.318(3) Å and V = 3834.37 Å3
Aluminocerite-(Ce)
IMA Number: 2007-060
IMA List formula: (Ce,REE,Ca)9(Al,Fe3+)(SiO4)3[SiO3(OH)]4(OH)
Generalised formula: (Ce,#)9(□,#)(Al,#)(SiO4)3[SiO3(OH)]4(OH)3
Original description: Nestola et al. (Reference Nestola, Guastoni, Cámara, Secco, Dal Negro, Pedron and Beran2009)
Type locality: Ratti quarry, near Baveno, Italy
Crystal structure: Nestola et al. (Reference Nestola, Guastoni, Cámara, Secco, Dal Negro, Pedron and Beran2009)
Unit-cell parameters: a = 10.6450(10) Å, c = 38.019(5) Å and V = 3730.98 Å3
Taipingite-(Ce)
IMA Number: 2018-123a
IMA List formula: (Ce7Ca2)Σ9Mg(SiO4)3[SiO3(OH)]4F3
Generalised formula: (Ce,#)9(□,#)(Mg,#)(SiO4)3[SiO3(OH)]4F3
Original description: Qu et al. (Reference Qu, Sima, Fan, Li, Shen, Chen, Liu, Yin, Li and Wang2020)
Type locality: Taipingzhen REE deposit, North Qinling Orogen, Central China
Crystal structure: Qu et al. (Reference Qu, Sima, Fan, Li, Shen, Chen, Liu, Yin, Li and Wang2020)
Unit-cell parameters: a = 10.7246(3) Å, c = 37.9528(14) Å and V = 3780.4(3) Å3
Merrillite
IMA Number: pre-IMA mineral
IMA List formula: Ca9NaMg(PO4)7
Generalised formula: (Ca,#)9(Na,#)(Mg,#)(PO4)7
Original description: Wherry (Reference Wherry1917)
Type locality: Alfianello meteorite, Alfianello, Brescia Province, Lombardy, Italy
Crystal structure: Xie et al. (Reference Xie, Yang, Gu and Downs2015)
Unit-cell parameters: a = 10.3444(3) Å, c = 37.0182(11) Å and V = 3430.5(2) Å3
Ferromerrillite
IMA Number: 2006-039
IMA List formula: Ca9NaFe2+(PO4)7
Generalised formula: (Ca,#)9(Na,#)(Fe2+,#)(PO4)7
Original description: Britvin et al. (Reference Britvin, Krivovichev and Armbruster2016)
Type locality: Shergotty Martian meteorite, Gaya District, Bihar, India
Crystal structure: Britvin et al. (Reference Britvin, Krivovichev and Armbruster2016)
Unit-cell parameters: a = 10.372(2) Å, c = 37.217(13) Å and V = 3467(3) Å3
Keplerite
(Complete paper not yet published)
IMA Number: 2019-108
IMA List formula: Ca9(Ca0.5□0.5)Mg(PO4)7
Generalised formula: (Ca,#)9(Ca,#)(Mg,#)(PO4)7
Original description: Britvin et al. (Reference Britvin, Galuskina, Vlasenko, Vereshchagin, Bocharov, Krzhizhanovskaya, Shilovskikh, Galuskin, Vapnik and Obolonskaya2020)
Type locality: Marjalahti meteorite, Viipuri, Pitkyaranta mining district (Pitkäranta mining district), Ladoga Region, Republic of Karelia, Russia
Crystal structure: Britvin et al. (Reference Britvin, Galuskina, Vlasenko, Vereshchagin, Bocharov, Krzhizhanovskaya, Shilovskikh, Galuskin, Vapnik and Obolonskaya2020)
Unit-cell parameters: a = 10.3330(4) Å, c = 37.0668(24) Å and V = 3427.4(3) Å3
Matyhite
IMA Number: 2015-121
IMA List formula: Ca9(Ca0.5□0.5)Fe2+(PO4)7
Generalised formula: (Ca,#)9(Ca,#)(Fe2+,#)(PO4)7
Original description: Hwan et al. (Reference Hwang, Shen, Chu, Yui, Varela and Iizuka2019)
Type locality: D'Orbigny meteorite, Coronel Suárez, Buenos Aires Province, Argentina
Crystal structure: not determined
Unit-cell parameters: a = 10.456(7) Å, c = 37.408(34) Å and V = 3541.6(4.8) Å3
Whitlockite
IMA Number: pre-IMA species
IMA List formula: Ca9Mg(PO3OH)(PO4)6
Generalised formula: (Ca,#)9(□,#)(Mg,#)[PO3(OH)](PO4)6
Original description: Frondel (Reference Frondel1941)
Type locality: Palermo No. 1 Mine, Groton, Grafton Co., New Hampshire, USA
Crystal structure: Calvo and Gopal (Reference Calvo and Gopal1975)
Unit-cell parameters: a = 10.330(2) Å, c = 37.103(5) Å and V = 3428.785Å3
Strontiowhitlockite
IMA Number: 1989-040
IMA List formula: Sr9Mg(PO3OH)(PO4)6
Generalised formula: (Sr,#)9(□,#)(Mg,#)[PO3(OH)](PO4)6
Original description: Britvin et al. (Reference Britvin, Pakhomovskii, Bogdanova and Skiba1991)
Type locality: Kovdor Zheleznyi Mine (Iron Mine), Kovdor Massif, Murmansk Oblast, Russia
Crystal structure: not determined
Unit-cell parameters: a = 10.644(9) Å, c = 39.54(6)Å and V = 3880 Å3
Wopmayite
IMA Number: 2011-093
IMA List formula: Ca6Na3□Mn(PO4)3(PO3OH)4
Generalised formula: (Ca,#)9(□,#)(Mn,#)[PO3(OH)]4(PO4)3
Original description: Cooper et al. (Reference Cooper, Hawthorne, Abdu, Ball, Ramik and Tait2013)
Type locality: Tanco Mine, Bernic Lake, Lac-du-Bonnet area, Manitoba, Canada
Crystal structure: Cooper et al. (Reference Cooper, Hawthorne, Abdu, Ball, Ramik and Tait2013)
Unit-cell parameters: a = 10.3926(2) Å, c = 37.1694(9) Å and V = 37.1694(9) Å3
Hedegaardite
(Complete paper not yet published)
IMA Number: 2014-069
IMA List formula: (Ca,Na)9(Ca,Na)Mg(PO4)6(PO3OH)
Generalised formula: (Ca,#)9(Ca,#)(Mg,#)[PO3(OH)](PO4)6
Original description: Witzke et al. (Reference Witzke, Phillips, Woerner, Coutinho, Färber and Contreira Filho2015)
Type localities: South slope of Punta de Lobos, Rio Seco, ~90 km south of Iquique, Tarapacá, I Region, Chile, and Cerro Mejillones, Mejillones Peninsula, Mejillones, Antofagasta, II Region, Chile
Crystal structure: Witzke et al. (Reference Witzke, Phillips, Woerner, Coutinho, Färber and Contreira Filho2015)
Unit-cell parameters: a = 10.3519(9) Å, c = 37.064(5) Å and V = 3439.7(6) Å3