American Mineralogist, Volume 67, pages 599403, l9E2

Cascanditeand jervisite, two new scandiumsilicates from Baveno, Italy

M. MeLI-tNr, S. MenuNo, P. OnraNor

Istituto di Mineralogia e Petrografia, Universitd di Pisa and C.NR., C.S. Geologia Strutturale e Dinamica dell' Appennino, via S. Maria 53, 56100 Pisa, Italy

AND R. Rrnelor

Istituto di Mineralogia e Petrologia, Universitd di Modena, viq S. Eufemia 19, 46100 Modena, Italy.

Abstract

Two new silicate , cascanditeand jervisite, were found as small crystals in a geode from Cava Diverio, Baveno, Italy. CascanditeCa(Scs.7aMg0.02Al0 0rFeE.l2)(Nao.orCao o+Mns.1sns.s5)SirOs.oz(OH) or ideally CaScSirOeOH, has triclinic symmetry, space group PI with lattice dimensions a : 7.529(lDA, b = 7.051(12)A, . : 6.755(9)A,a: 92'7'(5), F : 93"40'(5), y = 104'39'(5). The X-ray powder diffraction pattern has the strongestreflections at d = 3.62(mX200)'3.10(m) (20l,l2l,ol2), 2.968(m)(02l,lo2,ol2),2.821(s)(120), 1.429(m). Cascandite is structurallv related to the wollastonite-pectolite-seranditegroup of minerals. Jervisite (Nao.r:CaorrFeE.lnlo.rJ(Sco orne6jslr,tg6.le)Si2O6 has monoclinic symmetry, spacegroup C2lc withlattice dimensionsa :-i.ssjtrrlA" b :9.042(10)A,, : 5.312Q)4, F = 106'37'(7). The X-ray powder diffraction pattern has the strongest reflections at d : 6.5l(wxl10), 4.51(wX02l,lll), 3.038(s)(221),2.979(m)(310), 2.543 (m)(22r,002)' 1.647(m)(531,440).Jervisite is a scandiumpyroxene and a naturalanalogue ofthe synthetic phase NaScSi2O6.

Introduction phases, a scandium pyroxenoid and a scandium pyroxene, respectively.For theseminerals we pro- We have recently studied some small crystals posed the names cascandite from the chemical that occur in the granite from Baveno, Itiily. The composition and jervisite in honor of William P. sample was obtained through the kindness of Dr. Jervis, who was curator of the Museo Industriale Enzo De Michele of the Museo Civico di Storia Italiano di Torino and author of the book "I Tesori Naturale, Milan. The crystals are platy in habit sotterranei dell' Italia" on italian minerals. The new (Fig. 1), light pink in color, and are associatedwith minerals and their names were approved by the quartz, orthoclase and albite. The results of a I.M.A. Commissionon New Minerals and qualitative energy dispersive analysis, which Names. showed scandium as a major component, led to further study. A subsequent electron microprobe analysis, made on various crystal fragments,clearly X-ray crYstallograPhY indicated the presenceof two different phases,both rich in scandium, but differing in and calci- Rotation and Weissenbergphotographs indicate um content. that cascanditeis triclinic, with unit cell parameters - : We then reexamined the sample and found addi- a :'7.5A, b - 7.lA,c - 6.84, a 92o,F 93",y- jervisite tional platelets that were light green in color. The 104", space ggoup Pl or Pi; whereas is - results of the X-ray crystallographicstudy, together monoclinic with unit cell parametersd 9.84, b: with the microprobe analytical data and the results 9.0A, c - 5.3A, F - 107",with spacegroup CLlc or of the subsequentcrystal structure analyses,clearly Cc, on the basis of the systematicabsences (ftkl indicated that the pale pink and the light green absentfor h + k:2n + l, hDlabsent for l: 2n t platelets corresponded to two distinct mineral 1). Space groups P1 and CLlc, for cascandite and 0003-004K82/0506-059$02.00 599 600 MELLINI ET AL,: CASCANDITE AND JERVISITE

Table I gives the X-ray powder diffraction pat- tern for cascandite.Because of the small quantity of available material, we obtained the powder pattern by the Gandolfi tech^niquewith Ni-filtered CuKc radiation (I : 1.5418A),using a smallcrystal previ- ously examined by single crystal methods. The same crystal was used to collect the intensity data for structure refinement (Mellini and Merlino, 1982). In addition, single crystal intensity data offered a check on the indexing of the powder pattern lines. Table 2 compares the X-ray powder diffraction pattern of jervisite and the synthetic scandium analogue of aegirine, which was synthesizedby Ito l-,-l 7 rrrm and Frondel (1968).The powder patterns, obtained Fig. 1. Tuft in the center of the photograph is composed of by means of a Gandolfi camera with crystals previ- platy crystals of jervisite and cascandite. ously examinedwith rotation and Weissenbergpho- jervisite, respectively, were subsequently con- firmed by the structure analysis. Table l. X-ray powder diffraction pattern ofcascandite The crystals of cascanditeare pale pink platelets with vitreous luster, elongated along [100] and Cas cand i te Cascandite flattenedparallel to {001},with good and {100} {001} d (A) hk1 d(A) hkl cleavages.The dimensionsof the platelets are up to I 7 -22 100 122 0.20 x 0.08 x 0.02 mm, with 2.249 observedforms {001} 003 {100}, {120}, and {530} as shown in Figure 2. The 6.75 001

only optical propertiesmeasured w€r€ n1 (: 1.663) 4.46 llo 2.220 220

and,n2 (: 1.684)on (001). 3.84 111 1o3 2.rgo The crystals of jervisite are light green in color, 131

vitreous in luster, and have perfect (110). 3.62 200

Their habit and dimensions are similar to those of o20 32L

cascandite. oo2 2.t54 o13

3.25 2It 221

3.14 IO2 32I 2.128 3lo

201

3.10 r21 2.060 22r

ot2 2.O40 302

o2l t.779

2,964 102 t.7t7

o12 1.688

2.924 r.642 "r2 2.82I t20 t.623

2.753 2II 1.595

72L 1.564

2lI 1.524 2.59s tt2 L.447

2.42r 300 r.429 m

301 1 .398 2.337 \ o22 I .331

212 1.296 2.300 311 1.257 Fig. 2. Typical habit of cascandite. MELLINI ET AL.: CASCANDITE AND IERVISITE @l

Table 2. X-ray powder difrraction pattern ofjervisite and its synthetic analogue

j ervis ite NaScSi206 syn i ervis ite NaScSi2O6 syn

d (A) hk1 I d(A) I d(A) hk1 r d(A) I

t10 w 6,52 m 312 1.714 w o2I 1.6a9 O42 w 1,.697 m 4.51 w 4.52 m Itl 1.647 531 m 1.645 w

3.68 111 3.68 440 t .631 a

3.389 o21 w 3.39 u r.573 50O w I.579 w

220 u 3.25 v 351 7.564 w 602 3.038 22I s 3 .045 vs 1.549 wt 2.979 310 m 2,952 621

2.601 r31 w 2.607 1.528 4O2 w |.525 w 22I 332 n 2.523 1.511 w 002 060 400 622 2.304 w 2.329 t-4t| w 311 6ZO tt2 260 2,233 w 2'234 w l.4J) W 1.435 w o22 35r 330 152 2.t61 w 2.169 N 1,425 w 33r 531 243 2,132 421 w 2.135 L.397 w 2.067 04l- w 2.058 223 202 261 2.009 w I32 7t2

247 1.984 w 533

511 1,916 w lro w 1.336 u f.328 w 1.876 222 1.304 314 w 1.301 w 510 r.839 w 1.259 352 u 1.257 w r32 150 1.778 w 1.778 mv 421 tographs, were indexed using single crystal diffrac- reported in Table 4 as oxide weight percent. It was tometer data as a check. assumed that the iron present was Fe2+, and that The unit cell parametersfor cascanditeand jervi- the water content in cascandite corresponded to site were refined by a least squares method using one molecule in the unit cell, as indicated by the the powder pattern lines and axe reported in Table structural data discussed in the following para- 3, together with the unit cell parametersof synthetic graph. In Table 4 the cell contents for jervisite and NaScSizOo, as given by Hawthorne and Grundy cascandite are given, on the basis of three and two (re73). atoms in the unit cell, respectively.

Chemicalcomposition Structural and crystal chemical considerations Two crystal fragments, identified as cascandite The of cascandite was deter- and jervisite by X-ray single crystal methods, were mined by Mellini and Merlino (1982) and that of analyzed by electron microprobe. The standards jervisite by Mellini and Merlino and Rossi (to be used in the analysis were metallic scandiumfor Sc, published). The structures refined to R values of analyzed actinolite for Fe, Na, Mn, Ti. Raw data 0.M and 0.05, resPectivelY. were corrected by the ulcrc IV program of J. Jervisite is isostructural with the synthetic phase Colby. Three electron probe analyseswere madeon NaScSizOo, which was synthesized by Ito and each crystal fragment, and the average values are Frondel (1968),and whose structure was refined by 602 MELLINI ET AL,: CASCANDITE AND JERVISITE

Table3. Unit cell paxametersof cascandite,jervisite and its serandite. host different cations in casandite:one is synthetic analogue occupied by calcium and the other by scandium with minor Fe2* cations. The site where sodium cascandi te I ervis ite syn NaScSi2O6 cations are located in pectolite and serandite,has an extremely low occupancy in cascandite(Mellini and pl Space group C2/ c c2/c Merlino, 1982). a 1.s2e(r)X s.arr(tr)i s.a+:a(+)i The chemical contents reported in Table 4 can be b 7.O51 ( 11) 9.o42(ro) 9.0439(4) conveniently expressedby the formula: c 6.7ss(9) s.3r2(1) (2) 5.3s4o Ca(Scs.TaMg.ozAlo.orFeSlzMno.or) (Nao.or o 92" 7'(s') Cao.o+Mns.1sns.s5)Si308.02(OH). 0 93'4o'(s') 106'37r(7r) ro7.2L5" (2) The crystal chemical formula that better summa- ' Y 104'39' (5 ) rizes the chemical as well as the structural data is ca(sc3iM35xMA5!o 8)si3o8.2(oH)0.swith M2+ : (Fe2+,Mn2+),approximating the ideal composition CaScSisOs(OH). Hawthorne and Grundy (1973).From the chemistry (unit cell contents) given in Table 4, (Nao.+: Conclusions Cao.:r MNo.orFefr)e Mgs. r7 Scs.66 410.62 Tio.or)tot.: r.aq The two new mineral phases, cascandite and Si2O6.62,the following crystal chemical formula jervisite, join kolbeckite ScPOa.HzO, bazzite may be derived on the basis of structural data: Be3(Sc,Fe)2SioOrsand thortveitite (Sc,Y)2Si2O7,as (Na,Ca,Fe2*)1Sc,Mg,Fez*;Sirouwith Na rare minerals in which scandium occurs as an Ca,Fez*; Sc > Mg,Fe2*. Thusjervisite is a scandi- essential, major constituent. It seems remarkable um pyroxene, that is intermediatein the Ca(Mg,Fe) that three of the four scandiumsilicates were found Si2O6-NaScSi2O6series, analogousto the aegirine- in the granite of Baveno. The three other phases augite series. with relatively high scandium content (Sc2O32-6 Cascandite is structurally related to the wolla- vtt.Vo)are: Sc-ixiolite(Ta,Nb,Sn,Mn,Fe,Sc,. . .)zO+ stonite-pectolite-serandite group. The crystal (Borisenko et al., 1969),Sc-perrierite (Ce,La,Ca)a +,ScXTi,Fe3*)2Ti2( structure analysis clearly indicates that in cascan- (Fe2 O4l Sizo)z (Semenove t al., dite, as in pectolite and serandite, there is an 1966), magbasite KBa(A1,Sc)Fe2*Mg5F2Si6O2o intrachain hydrogen bond. The hydrogen atom was (Semenovet al.,1965). located by a difference Fourier synthesis. The two The rarity of scandium minerals is a result of its octahedral sites, which are both occupied by calci- crystal chemical behavior. In fact, in the first study um cations in pectolite and by manganesecations in of scandium geochemistry, Goldschmidt and Peter (1931)emphasized that the bulk of the elementis dispersed in very small amounts among minerals Table 4. Chemical composition of cascanditeand iervisite formed in the early stagesof magmatic differentia- tion, mainly pyroxenes, amphiboles and biotite. Oxide Weight per cent Element Atoms per forinula unit cascandite jervisite cascendite jervisite Only a very small amount passesthrough the mag- matic stage and enters pegmatitic, pneumatolitic sio2 51.83 50.42 si 3.OO 2.OO and hydrothermal deposits. t"2o3 18.48 Sc o.74 o,64 FeO 4.50 8.59 Fe o.22 o,29 Acknowledgment 0.20 2.80 o.02 o.t7 We are giratefulto Dr. F. C. Hawthorne for supplying crystals Tio2 0.08 0-55 Ti o.01 o.02 of the synthetic phase NaScSizOe,that were used for compari- A1-0- o. 11 o.42 o.o1 0.02 son. The electron microprobe at the Modena University was l{nO 2.32 o.44 Mn o.11 o.01 used in the present study and the Italian Consiglio Nazionale CaO 16.83 7.25 1.04 o.31 is acknowledgedfor its installation and mainte- Na2O o. 06 5.55 Na o.o1 o.43 l#:J.*"n"

<2.59) o 6,o2 "2o Il^o o.5 References Borisenko, L. F., Maksimova, N. V. and Kazakova. M. y. (1969)Scandium ixiolite, a new tantalum-niobatespecies with MELLINI ET AL.: CASCANDITE AND JERVISITE 603

formula (A,B)"O2". Doklady Akademie Nauk SSSR, 193,167- Mellini, M. and Merlino, S. (1982)Crystal structure of cascan- t70. dite. American Mineralogist 67, 604-6W. Goldschmidt, V. M. and Peter, C. (1931)Zur Geochemie des Semenov,Y. I., Khomakov, A. P. and Bykova, A. V. (1965) Scandium. Nachrichten von der kdniglichen Gesellschaftder Magbasite, a new mineral. Doklady Akademie Nauk SSSR, Wissenschaftenzii Gottingen-Geologie und Mineralogie IV, 163,7r8Jt9. 257-259. Semenov,Yl I., Kulakov, M. P., Kostynina,M. Y., Kazakova, Hawthorne, F. C. and Grundy, H. D. (1973)Refinement of the M. Y. and Dudykina, A. S. (1966) Scandium content in the crystal structure of NaScSi2O6.Acta Crystallographica,B29, quartz-fluorite pegmatites of Kazakhstan . Geol