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Cascandite and Jervisite, Two New Scandium Silicates from Baveno, Italy

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Cascandite and Jervisite, Two New Scandium Silicates from Baveno, Italy 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 minerals, 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 Mineral 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 sodium 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)cleavage. 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). silicon atoms in the unit cell, respectively. Chemicalcomposition Structural and crystal chemical considerations Two crystal fragments, identified as cascandite The crystal structure 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).
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