American Mineralogist, Volume 67, pages 599-603, 1982

Cascandite and jervisite, two new scandium silicates from Baveno, Italy

M. MELLINI, S. MERLINO, P. ORLANDI Istituto di Mineralogia e Petrografia, Universita di Pisa and C.NR., C.S. Geologia Strutturale e Dinamica dell' Appennino, via S. Maria 53, 56100 Pisa, Italy

AND R. RINALDI Istituto di Mineralogia e Petrologia, Universita di Modena, via S. Eufemia 19, 46100 Modena, Italy.

Abstract

Two new silicate , cascandite and jervisite, were found as small crystals in a geode from Cava Diverio, Baveno, Italy. Cascandite Ca(ScO.74MgO.02Alo.Ol Fe6.~2)(N ao.OlCao.o4Mno.l0Do.s5)Si30s.o2(OH) or ideally CaScShOsOH, has triclinic symmetry, space group PI with lattice dimensions a = 7.529(II)A, b = 7.051(12)A, c = 6.755(9)A,a = 92°7'(5), f3= 93°40'(5), 'Y = 104°39'(5).The X-ray powder diffraction pattern has the strongest reflections at d = 3.62(m)(200), 3.10(m) (201,121,012), 2.968(m)(021, 102,012), 2.821(s)(120), 1.429(m). Cascandite is structurally related to the wollastonite-pectolite-serandite group of minerals. Jervisite (Nao.43Cao.31Fe6.14Do.12)(SCO.66Fe6.15Mgo.19)Sh06has monoclinic symmetry, space group C2/c with lattice dimensions a = 9.853(II)A, b = 9.042(10)A, c = 5.312(7)A, f3 = 106°37'(7). The X-ray powder diffraction pattern has the strongest reflections at d = 6.51(w)(110), 4.51(w)(021, 111), 3.038(s)(221), 2.979(m)(310), 2.543 (m)(221,002), 1.647(m)(531,440). Jervisite is a scandium pyroxene and a natural analogue of the synthetic phase NaScSh06.

Introduction phases, a scandium pyroxenoid and a scandium We have recently studied some small crystals pyroxene, respectively. For these minerals we pro- that occur in the from Baveno, Italy. The posed the names cascandite from the chemical sample was obtained through the kindness of Dr. composition and jervisite in honor of William P. Enzo De Michele of the Museo Civico di Storia Jervis, who was curator of the Museo Industriale Naturale, Milan. The crystals are platy in habit Italiano di Torino and author of the book "I Tesori (Fig. 1), light pink in color, and are associated with sotterranei dell' Italia" on italian minerals. The new , and . The results of a minerals and their names were approved by the I.M.A. Commission on New Minerals and qualitative energy dispersive analysis, which . showed scandium as a major component, led to Names. further study. A subsequent electron microprobe analysis, made on various crystal fragments, clearly X-ray crystallography indicated the presence of two different phases, both rich in scandium, but differing in sodium and calci- Rotation and Weissenberg photographs indicate um content. that cascandite is triclinic, with unit cell parameters We then reexamined the sample and found addi- a::::::7.5A, b::::::7.1A, c:::::: 6.sA, a:::::: 92°, 13::::::93°, '}':::::: tional platelets that were light green in color. The 104°, space group PI or pi; whereas jervisite is results of the X-ray crystallographic study, together monoclinicwith unit cellparameters a ::::::9.sA, b :::::: with the microprobe analytical data and the results 9.oA, c ::::::5.3A, 13::::::107°, with space group C2/c or of the subsequent analyses, clearly Cc, on the basis of the systematic absences (hkl indicated that the pale pink and the light green absent for h + k= 2n + 1, hOl absent for l = 2n + platelets corresponded to two distinct mineral 1). Space groups pI and C2/c, for cascandite and 0003-004X182/0506-0599$02.00 599 ~--

600 MELLINI ET AL.: CASCANDITE AND JERVISITE

Table 1 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 technique with Ni-filtered CuKa radiation (A= 1.5418A),usinga 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 synthesized by Ito 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 examined with rotation and Weissenberg pho- jervisite, respectively, were subsequently con- firmed by the structure analysis. The crystals of cascandite are pale pink platelets with vitreous luster, elongated along [100] and flattened parallel to {001},with good {100} and {001} cleavages. The dimensions of the platelets are up to 0.20 x 0.08 x 0.02 mm, with observed forms {001} {100}, {120},and {530}as shown in Figure 2. The only optical properties measured were nl (= 1.663) and nz (= 1.684) on (001). The crystals of jervisite are light green in color, vitreous in luster, and have perfect (110) . Their habit and dimensions are similar to those of cascandite.

a 1

Fig. 2. Typical habit of cascandite. MELLINI ET AL.: CASCANDITE AND JERVISITE 601

Table 2. X-ray powder diffraction pattern of jervisite and its synthetic analogue

jervis i te NaScSi206 syn jervisite NaScSi206 syn

d(A) hk1 d(A) d(A) hk1 d(A) 6.51 110 6.52 312 1. 714 021 1. 689 042 1. 697 4.51 4.52 111 1.647 531 1.645 3.68 111 3.68 440 1.631 3.389 021 3.39 1.573 600 1. 579 3.255 220 3.25 351 1. 564 3.038 221 3.045 vs 602 1.549 2.979 310 2.952 621 2.607 131 2.607 1. 528 402 1. 525 221 332 2.543 2.523 1.511 vw 002 060 400 622 2 . 304 2.329 1.471 311 620 112 260 2.233 2.234 1. 435 1.435 022 351 330 152 2. 161 vw 2.169 1.425 331 531 2.132 421 2.135 243 1. 397 2 . 067 041 2 .068 223 202 261 2 .009 132 712 1. 352 241 1. 984 vw 533 1.922 511 1. 916 710 1. 336 1. 328 422 1. 876 621 222 1 . 304 314 1.301 510 1. 839 1.259 352 1. 257 132 150 1.778 1. 778 421 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 parameters for cascanQite and 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 are reported in Table structural data discussed in the following para- 3, together with the unit cell parameters of synthetic graph. In Table 4 the cell contents for jervisite and NaScSiz06, as given by Hawthorne and Grundy cascandite are given, on the basis of three and two (1973). silicon atoms in the unit cell, respectively. Chemical composition 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 scandium for Sc, published). The structures refined to R values of analyzed actinolite for Fe, Na, Mn, Ti. Raw data 0.04 and 0.05, respectively. were corrected by the MAGICIV program of J. Jervisite is isostructural with the synthetic phase Colby. Three electron probe analyses were made on NaScSiz06, 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

Table 3. Unit cell parameters of cascandite, jervisite and its serandite, host different cations in casandite: one is synthetic analogue occupied by calcium and the other by scandium with minor Fez+ cations. The site where sodium syn cascandi te jervisite NaScSi206 cations are located in pectolite and serandite, has an extremely low occupancy in cascandite (Mellini and Space group P1 C2/c C2/c Merlino, 1982).

7.529 (ll)A 9.853(1l)A 9.8438 (4)A The chemical contents reported in Table 4 can be ( 7.051(11) 9.042 (10) 9.0439 4) conveniently expressed by the formula: 6.755(9) 5.312(7) 5.3540(2) Ca( SCOt74M~ .0zAlo.01F eij~zMno.o 1) (N ao.OlCao.04Mno.loDo.8s)Si308.0Z(0 H). 92° 7'(5') 93°40' (5') 106°37'(7') 107.215°(2) The crystal chemical formula that better summa- 104°39'(5') rizes the chemical as well as the structural data is Ca(Scij~Mij~)(Mij~Do.8)Si308.z(OH)0.8 with MZ+ = (Fez+ ,Mnz+), approximating the ideal composition CaScSi308(OH). Hawthorne and Grundy (1973). From the chemistry (unit cell contents) given in Table 4, (Nao.43 Conclusions Ca.o.31 MNo.01 Feij~9MgO.17 SCO.66 Alo.oz Tio.01)tot.=1.89 The two new mineral phases, cascandite and Siz06.oz, the following crystal chemical formula jervisite, join kolbeckite ScP04' HzO, bazzite may be derived on the basis of structural data: Be3(Sc,Fe)zSi6018 and thortveitite (Sc,Y)zSiZ07,as (Na,Ca,Fez+)(Sc,Mg,Fez+)Siz06 with Na > rare minerals in which scandium occurs as an Ca, Fez+; Sc > Mg,Fez+. Thus jervisite is a scandi- essential, major constituent. It seems remarkable um pyroxene, that is intermediate in the Ca(Mg,Fe) that three of the four scandium silicates were found Siz06-NaScSiz06 series, analogous to the aegirine- in the granite of Baveno. The three other phases augite series. with relatively high scandium content (SCZ032-6 Cascandite is structurally related to the wolla- wt.%) are: Sc-ixiolite (Ta,Nb,Sn,Mn,Fe,Sc,. . ')Z04 stonite-pectolite-serandite group. The crystal (Borisenko et al., 1969), Sc-perrierite (Ce,La,Ca)4 structure analysis clearly indicates that in cascan- (Fez+ ,Sc)(Ti,Fe3+)zTiz(OJSiz07)z (Semenov et al., dite, as in pectolite and serandite, there is an 1966), magbasite KBa(Al,Sc)Fez+MgsFzSi60zo intrachain hydrogen bond. The hydrogen atom was (Semenov et 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 manganese cations in of scandium geochemistry, Goldschmidt and Peter (1931) emphasized that the bulk of the element is dispersed in very small amounts among minerals Table 4. Chemical composition of cascandite and jervisite formed in the early stages of magmatic differentia- a___ tion, mainly pyroxenes, amphiboles and biotite. Oxide Weight per cent Element Atoms per forinu1a unit cascandite jervisite cascandite jervisite Only a very small amount passes through the mag- matic stage and enters pegmatitic, pneumatolitic Si02 51.83 50.42 Si 3.00 2.00 and hydrothermal deposits.

Sc203 14.74 18.48 Sc 0.74 0.64 FeO 4.50 8.59 Fe 0.22 0.29 Acknowledgment ~.!gO Mg 0.20 2.80 0.02 0.17 We are grateful to Dr. F. C. Hawthorne for supplying crystals Ti02 0.08 0.55 Ti 0.01 0.02 of the synthetic phase NaScSi206, that were used for compari- A1Z03 0.11 0.42 A1 0.01 0.02 son. The electron microprobe at the Modena University was MnO 2.32 0.44 Mn 0.11 0.01 used in the present study and the Italian Consiglio Nazionale CaO 16.83 7.25 Ca 1.04 0.31 delle Ricerche is acknowledged for its installation and mainte-

Na20 0.06 5.55 Na 0.01 0.43 nance.

H2O (2.59) 8.54 6.02

H2O 0.5 References Borisenko, L. F., Maksimova, N. V. and Kazakova, M. Y. (1969) Scandium ixiolite, a new tantalum-niobate species with MELLIN I ET AL.: CASCANDITE AND JERVISITE 603

formula (A,B)nOln. Doklady Akademie Nauk SSSR, 193, 167- Mellini, M. and Merlino, S. (1982) Crystal structure of cascan- 170. dite. American Mineralogist 67, 604-609. Goldschmidt, V. M. and Peter, C. (1931) Zur Geochemie des Semenov, Y. I., Khomakov, A. P. and Bykova, A. V. (1965) Scandium. Nachrichten yon der koniglichen Gesellschaft der Magbasite, a new mineral. Doklady Akademie Nauk SSSR, Wissenschaften zii Gottingen-Geologie und Mineralogie IV, 163, 718-719. 257-259. Semenov, YI 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 NaScSh06. Acta Crystallographica, B29, quartz- of Kazakhstan. Geokhimiya 2, 244- 2615-2616. 246. Ito, J. and Frondel, C. (1968) Syntheses of the scandium analogues of aegirine, spodumene, andradite and melanote- Manuscript received, July 9, 1981; kite. American Mineralogist 53, 1276-1280. accepted for publication, November 23, 1981.