American Mineralogist, Volume 61, pages l0B-l 15, 1976

The crystal structureof tetragonalleucite

FronENzo Mtzzt, C.N.R. Centro di Studio per la Cristallografia stnttturale, c/o Istituto di Mineralogia dell'Uniuersitd, pauia, Italy

EnnreNr.roGALLT, nNn Gt-,luco Gorre,Ror Istituto di Mineralogia e Petrologia dell'Uniuersitit, V[odena, Italy

Abstract Low temperatureleucite is knownto havea tetragonalstructure which is similar to thehigh temperaturecubic structure.This tetragonalstructure has never been studied because of the finetwinning, which makes the selection of untwinnedsingle crystals difficult. The best crystal chosenfor this researchis madeup of threeindividuals: one, comprising 79 per centof the total,is merohedricallytwinned with respectto thesecond, and pseudo-merohedricallywith respectto the third.The crystalstructure of tetragonalleucite, a: 13.o9,c: 13.75A, space EroupI4r/a, can be derivedby displacingthe cubic structure (some atoms must be shiftedas muchas l A;. Thereis no (Si,Al)order. The K atomsare coordinated by six oxygensat the averagedistance of 3.01A, sixother being at -3.7 A.ln cubicleucite these values are 3.35 and 3.54A; this is the moststriking difference between the crystalstructures.

Introduction the chemical analysis also revealedthe presenceof Leucite K[AlSi,O6] was shown by Wyart (1940)to 0.002 Mg and Ti. have a structure with the same topology as analcime, The unit cell dimensionsand the intensitiesof the as determinedby Taylor (1930).Leucite undergoesa reflections were measured with a Philips rwrroo phase transition, also described by Wyart (1940), singlecrystal automatic diffractometerusing graphite from a cubic phase (space group la3d) stable above monochromatized MoKa radiation at room 630"C, to a tetragonal one (space group l4r/a) stable temperature.The cell dimensionsthus determined-a : : at lower temperature. This polymorphic inversion 13.09(l)and c 13.75(1)A-are in good agree- was investigatedin detail by Faust (1963),who also ment with those determined by the least-squares listed previous studies of the problem. Recently refinementof powder diffraction data and with those Peacor(1968) refined the structureofthe cubic phase quoted by Faust (1963) for a sample from the same of leucite at high ternperature. The same author locality. The space group determined from the pointed out the difficulty of obtaining a suitable systematic absencesis I4r/a, the same as determined single crystal of the tetragonal phase due to the fine by Wyart (1940)and by Ndray-Szab6(1942). The in- twins which alwaysdevelop in tetragonalleucite dur- tensitiesof 1040independent reflections in the range ing its inversion from the high temperature cubic 4o-50" 20 were inspected using 0-20 scans with a phase. symmetrical scan range of 1.20' in 2d from the calculated diffraction angle. The scan rate was 0.04o Experimental 0/sec. For each reflection,repeated scans were made until the preset maximum number (3) or the preset A sample of leucite from Roccamonfina,Caserta, number of counts (1000) was reached. Due to the Italy (specimen n. 16-3-3-24 of the Museo di small dimensions(0.05 X 0.05 X 0.08 mm) of the Mineralogia dell'Universitddi Modena) was selected crystal, 529 weak reflections were skipped by the for this study (seenext section).A chemicalanalysis diffractometer program during the data collection, of this materialyields unit cell contents,calculated on becausetheir intensitiesin counts,/sec the basis of 6 oxygens,ot measuredat the top of each reflection (namely, ,lt) and the mean I 6([ Ko aoorCao o,] Fef, Si, intensities ".N [ .+o,Alo.r"]orO. ); in counts,/sec of both backsround 108 CRYSTAL STRUCTURE OF TETRAGONAL LEUCITE 109 measurements (namely, 15) gave: Irzrt< Ib. merohedricallytwinned individuals,the first compris- These "unobserved" reflections were assignedvalues ing 88 percent,the second8 percent,and the third 4 of half the minimum observedintensity. Three stan- percent; the second fragment, composed of only two dard reflections, monitored at three hour intervals, pseudomerohedricallytwinned individuals, compris- showed no variation in intensity greater than I per- ing 96 and 4 percent respectively,was satisfactory for cent. Processingof the data was carried out in the further measurements.The first individual of the twin manner describedby Daviesand Gatehouse(1973) to was actually affected by merohedric twinning, which the refinement of the crystal yield lF.u"l and olF,o"l. No absorption or extinction was detected during corrections were applied. The atomic scattering fac- structure (see next section). tors used are those listed by Hanson et al (1964). If a twinned crystal of tetragonal leucite is heated above 630oC,it inverts to an untwinned cubic crystal The leucite twins which, upon lowering the temperature, gives a Natural leucite crystalsalways grow as the cubic twinned crystal again with the same proportion of phase (Faust, 1963). When a cubic leucite single- twin domains and with the same twin boundaries as crystal inverts to the tetragonal form, a complex twin before. This "memory" displayed by leucite twins develops.All six planesof the cubic form {110} may was demonstrated by optical and/ or X-ray. methods become twin planes in the tetragonal phase (point by Wyart (1938), Peacor (1968), Sadanaga and group 4/m). Two casesmust be considered: Ozawa (1968), and Korekawa (1969). This I. Merohedric twins develop on the tetragonal "memory" was verified once more during this planes(110) and (T10),the two individualshaving ex- research, on the following three twins: actly parallel crystallographic axes, but with a and b I. Two individuals with common a axis, kept at interchanged. X-ray diffraction of such twins gives 800'C overnight. hkl diffractions of one individual exactly superposed II. Four individuals with common a axis, kept at -630'C with khl diffractions of the other. The two in- 700"C overnight,and then for threehours at dividuals of the twin show simultaneousextinction before cooling to room temperature. under crossednicols. III. Four individuals,the a axis being common for IL Peudomerohedric twins develop on the two individuals at a time, were kept at 700"C for one quenchings to room tetragonal planes ( l0l ), (0 I I ), ( 101), (0 I I ), the two day, with four interspersed fast individuals having parallel a (or b) axes, but the temperature. remaining two axes are not parallel. The two in- The intensities of a small set of diffractions were dividuals of such a twin give close but distinct spots measured at room temperature before and after in X-ray photographs and do not extinguish simul- heating for each twin individual; there was no signifi- taneouslywhen viewed under crossednicols. cant variation of these intensities. In short, if singlecrystal X-ray photographsreveal Determination and refinement of the any splitting of spots, at least a pseudomerohedric crYstal structure twin is presenqif no splitting appears,the presenceof a merohedric twin may still be suspected,but it can The structural study started with the atomic be detected only by studying the intensitiesof the parameters given by Peacor (1968) for the cubic diffractions. phase, properly adapted to the tetragonal space The different orientations of the individuals in group. Least squaresrefinement with a modified ver- leucite pseudomerohedrictwins were described in sion of the program Onnm (Busing, Martin and detail by Sadanaga and Ozawa (1968) and by Levy, 1962) allowed the reduction of R from 0.54 to Korekawa (1969). only 0.32, without possibility of further improve- Since the observation of the pseudomerohedric ment. Direct methods (program MulrnN described twins is properly made using the polarizing by Germain, Main, and Woolfson, l97l) were then microscope,thick sectionswere prepared from our applied, and new starting parameters were obtained. leucite specimen to allow the selection of some ap- In this case,R dropped to 0.1I in four least-squares parently untwinned fragments. Most of these frag- cycles. after a first X-ray test with os- At this stage one point emerged: the largest ments were discarded 's cillation photographs, but two were thus selected. differences between lF o"l and lF"'t"l were Measurementsusing the singlecrystal diffractometer observed for pairs of F1,p1and Fnntwhen lF""r"l's of revealed the first to be composed of three pseudo- the two were markedly different. This was ascribedto ll0 MAZZI, GALLI, AND GOTTARDI

Trnlp l. Observedand CalculatedStructure Factors rtlrolls"lhtlrollF"lhklp"ilr"lhklF)lr"lhklpollF"lhklF"llF"lhklr"llr"l

2 9 206 411 L2* 246 -427 6 0 44-t -457 r0 3 90t -877 2 8 lO71 -tO9O r=6 4 9 -AS9 -1463 2 0 485 499 792 t2, 252 -t?6 I 0 1439 12 3. 258 -14,9 4 I 108.9 _II:,O -'-.. 4 0 6854 -6856 6 9 571 531 12* 26.2 3.8 L0 O' 22.4 32,7 14 3 75,2 7O.A 6 3 s7.a sj j ",:, 256.3 3 6 0r 16t -102 9 596 592 t2j 2j .S _t,4 12 0a 24.9 -S77 I 0 1945 1962 t0 9 585 14 tii,i-tii,i -452 o*27 s i"; I0 0 ll45 -1I90 l2 9t 242 ,;. ,;: ,;. l i ll:l il 9 lirz a'!. ii,i2aa '129ii,i i i 13* 26r -s69 I I 386 421 s 4 +.i -i.s ;;. ,i'.; i;.; 12 0 659 -685 I I0 2t24 2274 l3r 269 -194 3 I I774 176l 7 4. 207 _LL6 I 9 A22 -8gI lO or 249 _4r9 14 0" 268 388 3 l0 103 I -103 9 -189 s I -327 13. 280 356 9 4, 2?a -262 3 9) 229 116 12 O* 271 22r s l0 159 8 -160 -1891 2 2 488 468 9 7 I l89l tI 4 723 682 5 9* 239 373 7 t0 191 'i.! 4 2 3974 5883 125 '3 a. 21.3406 9 l0 855 833 i;. i:; j]i j:I I i ,i11';;; 6 2 E75 940 -,ta ,i i' Jli ; :: i:i ;il.i 8 2 2963 -3007 It I0r 280 17 ii i. :;; i:) ; i 24.7 l:: i::tai 4r j, _;;; 4? s2 er3l: -e6i1!? ,? ;' ::; :;i t i riii ,.,n l0 2 106l 1053 2 ll 2a4 l!" i; ;;; ?05 I5r 2a7 12 6 S. 204 -t2 2 IOr 237 35? 9 1 44\ L2 2* 24,4 43 9 4 ltr 238 189 t 2- 142 153 8 5 tot8 1018 4 t0, 244 319 ll I 8s6 _Rts t4 2 146 -776 6 ll 425 406 L-3 14O 25s l0 5* 244 ,t8 6 I0r 255 -31? l3 1r 2A7 _2s6 8 lt 796 2 4 1303 t30l 749 t2 s' 266 -3s7 l0 11* 260 360 ! j 22' ,eo -206 4 4 22L2 2283 9 119 qi199 j 'il:f il.i 46e -4es ,:l::r0 r0' 28si:: 206t:: 6 4 250 -184 -Sa I tir ,3 ii6.i il:.i I ! ;i ii.l -*.. t2r 24 3 I _;i.; 3 6 4ro so2 | tt. 247 li2 6 2 440 _4s7 8 4 23A 134 t2* 211 9 9!J ls8 i, ,. ;;.; 194 0 rjsr r33, s o. 204 16o 1 r 604 60l a 2 aEo -s46 l0 4 tl30 tI02 12 679 640 i;- ,. ):,: 3;; 0 1482 1499 7 6' 220 -296 5 tl 663 -692 tO 2 804 aao 12 4 635 -731 12* 26 1 -44 S o. 233 -266 r r 9 6' 239 409 1 Ll" 27t _329 72 2. _77 t4 4| 275 -2!9 -20 273 L2r 2A 2 a 91 259 _2Sa 3 3 1044 -1058 ll 6 474 382 9 tI 55S 549 -20 7^?l -992 2 6 1865 -1867 13' 257 14 5 o* 28s o6 s 3' 17s lJ 6 66s -627 ,.:. ,,." l: 7 "," 4 6 2t2A -2016 t3* 263 238 3 1546 1548'-i ^ ^ I t2.' -2-- 2 1' r9.8 -41.2 4 t2, 26.6 4J." s t" 2t.o _7.3 6 6' 203 -430 t3. 27 3 -24 2 s i it.6 - | 58.7 49.2 ti i riss _,oin 4 1' 20.7 -4t.7 b ll. 27.o -34.o 7 3 r2i.6 -130.2 3 6 I394 1402 13. 285 tl9 .41.! '_' I ta 6* 231 466 l, 1!.: ii i. ,;; -i:;_ t al.o 11.1 ! t!' !!.! li e 3* 24.4 4.0 14 990 1029 Ii 196 4t I 7 1499 l5O4 \ t3' 271 235 tt 3 1399 1379 t2 6a 260 292 2 -292 14 857 882 | 734 193 4' 159 1O 7' 256 431 3 r3r 2?5 3i 13 3* 2A.6 22O 14 61 285 -395 4 -147.9 t4* 2AO 55 9 l. 24.6 -6.3 4 \40,1 12 7 36,9 52.9 5 l3r 28,2 ,10,3 -65.2 6 4 51,5 52-5 '28t28.s 61.9 66.4 2 8r 25,0 11 isi 284 200 | 72,4 s" 2 14*14' s -s0-so.s s 4 8 -1404 a 4 e3.B ii.i \ 20.7 rs.e i i li.i 7j.3 1399 t5r 289 1a 2 1082 -1122 8* -41 -t2tl tO a 804 -79.3 3 212 6 4 967 -94J 6 3 1161 ztal tous s 8 J73 3oB a -hrn 8 8* 233 _255 I iz o. 1i.i _i." 8 o6.s 2 1314 L22a j6) 1 I 2-o _r2j I 0 b?- bo ,o 4 cr6 Indn l0 I 575 5A2 t;' i. _;; 2 0 E25 -833 2 l7g4 827 g A. 254 -245 3 O 6t9 638 t2 4r -24 L2 A' 21 4 St9 2?8 0 955 -936 2* 2tt 2. I 5 865 894 \r a* 271 43 S O 936 _984 I .266 7 836 2 l0+ 25_0 -tl 6 6 0r t65 233 8J4 -'7r s' r's -ill , o roi.6 -Lii.a l: 1 4 l0 766 4e.o 46.7 5 s n2.4 rrr.6 3es 700 8 0 692 694 : :" ii9 ; ;.';::;-li::: I !' ilo -er/ 6 190 -39 84.2 8r.r / s s43 s34 ri 6 ;;.) 870 l0 767 l0 0* 2lE I :- lll -:91li: it.) :: .ei.r 8 l0 101 2 -106 2 -120 e r 46.s -47.2 I l: i19 i: ;. :;.; -;;; 7 s ae.o t2 0* 244 2 13q,6 192,9 8 9. 25.4 -48.0 9 5. 25,2 l0 I0 122 6 -119 6 0. 270 183 -;; 20,3 rs.e 4o.r li ;, ;;; ro s. 27.2 4rs 2 | 32s i3e rr s, zii lit t2' 244 -251 L I ll08 -1058 6 117,5-118,4 4 I 387 362 gs ,:: -,:l 12 1528 1556 3 I 842 -831 8 Jo.l 50.3 I 6 4 _80 o : l.l I : r 464 42s t9?2 r914, :;.i 7.?-s. 4I 69 409 clo t2" ?60 s9 5 r 668 681 l0 ;;:; 4 6, is.r ;.: I 19 Z! ? I 670 So.o 5 t0 s3.0 52 5 i. :;; ";: 6 b+ 23.4 -51.3 t2* 274 -22A 7 r l2l0 I2t? r2 1' 2s.t JB.2 o o rru.o rol.o -1! r; ,625 3 se.o .so.e a 6 -ii.i I M:.1 I i; i.r. !;.;r^< _ri"-r;.; 8 o 49.24s.2 s6.3 14 40,3 41,6 I 615 9 l0 60 6 -52 5 _4.3 : -a1 IO b. ":.224.5 _2?.0 i. ;; ; _t; ; ro b. 2b.1 -87.4 lr 231 I '.29 14 a7.0 i: 1 !99 r: e. lol ruz 2 l* 244 rer i2 6" 2A7 -406 14 66.4 -12.2 I 458 435 3 4 4s3 37s :::_ :l: ::: j 2 s3o e47 i; t" 243 t6 5 4 7e.6 -.e.r | 7 il: -2o I ll: il9 1l: i i rii.i'iz.s rsr.. ! 7' 2so -too - -199 3 7 s8r -elr 2 2. t20 t09 7 4 I222rz22 _\!A3-t!at 3 7 1077ro71 ll4rI4.8 : 1l' i!9 i : -i".r 4 2 424 9 I 0 385 -405 410 ',8j:t'u3 jii j"'i"i '2ii 6 2 626 ,6\S ll 1 : ; i3l -3ji t l lit ij3 3 0* 115 196 i ii: iii " a 2 998 98I l3 4' 26.7Bs ';.: 5 0' t47 06 'ii iii; !ii _l!.i j. ro 2. 22A 205 ,1;' |i]'r\ 'jll 2* !;l27A 72 ,:,: 3i:3 !i3 0' 176 t48 s 33s ie s ':: t2 2 756 120 !:,13 l.i. il',2es _332 9 0 130 2 -134 I i ,jii ;jii-iii ,.,u0., _,u,., 6-16.r!e \4 21 212 62 I::. :l: : "^, iI 0f ?29 L1 6 s oi.i 2 a 2as 266 1 lit i!9 1l 8 i- ;3i ;;i I :, .l::r ::::: : 3' :i: *: l3 0. 2s5 468 I 3 695 689 'i3 'li:i j r"0." riio I I 20:9i -r3?11 l5 0* 282 -52 3 3 2?34 -26AL l0 i 11! I i. 13i {: : ,se.: iir." .l l' 3 r i i i !!' l! i l0 8 62462 4 -62r-62 5 3* 250 13l l2 5 5e.4 ss.s 8 8 3a.o .3s.3 s, zq.t _r).2 O 2 Il0 5 106 5 3i 14"i;. 2al: 3i -40:i:o 7 3 I296 1263 s, ze.s i;:3 ro 8. 2s.e i;.; 31 269 -45r I 9* 696 -6S2 239 \J 9 3a 21r -352 L2 8' 280- -113 ?t9 1\6 I 6 991 106z1062 L-6L-6 rI 4 t65i1653 -1680 I 9 693 777 II 3 685 -682 I lll I lto 7 3 6 rrs.3 123.0 | s. 21.3 -ri^.2 4s.6 -4i.3 ,1.2 Mr 26 1 4Sl 2z 0o rs4.3ls43 1546rs46 I 1 ::: :2: -7.9 l0 462 499 5 o sr.6 -48.9 J 9 sr.r -sa.l s i vi.i ';;.;t)r'i 26a 15 3' 287 'l:9 t191 : l2 406 -341 360 7 6 ro8.b -r7r.r , s" ru.e -io.i 1 9 ; ;;.; e s' 2-.s 6 0 948 _978 747 88 2 2 4 688 617 9 b' 23.1 -26.7 7 a 494 .a4 'il:: 'i::l jl 4 4 325 310 1l 6 633 62.2 s e* zs8 "i.1 ,?| I 1:!' 26.1? -17.4ll.] 4 l0' 2s./ -to.7 I 2 t57 2 -lS5 4 ,l :.n. ,; i -;i. -,^ i !8. ZZ', _iZi 6 4r t81 -160 I3 6 684 7A6 Il 9* ?7A rr rr 28.1 2' b 6 ro' 26.1 3 2 1286 1296 0r;. 259;; ; !43 J.J a 4, 204 -3!9 5 2 t05,1 -94 2 94 2 1 es7 -s7s 2 ro l2s4 r3os t4 or 283 -3?.8 2 s 274 -223 l0 4* 22A -230 I 19. l!9 2 130 5 -t3l 2 7 35.6 32.3 4 10 33,6 --i;', 12 4* 252 -i37 -4 2 449 337 i a2! 6 ,0 ^., l t' 1:1 t:.1 I i- li.l ?l:3 I li" !l:i !31 14 4* 277 r50 -- ll 2 1047 1105 3 z-.'.2s^ 8 0 80., ,91 j3i jil 10 i- 24.e .)a I l0 r0* 2-.7 4).4iti ; i ii:j i,i ,l ?ii: t3 2* 251 547 sr 153 66 ; i ';;:;rbi., rog.:';;.; ]: l., ljl I5 2 8I8 ,808 s 2536 t2 7* 27.o -21.6 12 s' 2?.6 r4.4 -13.o 23?2 1 rr s4.s -sl.s ; i 2 12' 27.3 5 -106 q 4 r2l 21 I -3 1 2 3 730 -684 lD? 4 I I 8 109.3 -rr2.s I ll s:.: -ii.i rL 11 24.? zz 5 189 7 -189 3 3\'? -17..\ 3* t41 60 3 8 6s8658 6186t8 t5 rr'llr ,ro2so lid230 L3 rr| 27.!271 -234-23.4 5 474 I ! _562 :1:,I l3' 2439:l -l7a::: 3 395 260 423 5 8 7 \r' 26.2 6 415 5 r049 13r.6r33.? 2 2* \6.6 0.6 -ifi i ij: 33i _ll3 8 3 553 580 1058 7 a' 22.9 40 r 9 1l' 27-a -70,4.!i : : lii 5 -504 4 2 85.7 ez.s i IO 3 ls4l I559 52t a 2a.2 32.3 2 r21 ?s.L u ,0r,, ,0,.a :1.! 6 2 113.7 rl3.s i u 78.0 77-s 2=s t2 3 553 627 6 274 2a2 ll 8'B, 26726? -3Ol_3ot 4 12'12, 667 -737_737 a z vzt -876 riZ.s ,; ; ;;.; ;;.; -33.8 l4 3 913 6* 181 262 t3 8r 28,9 -48.0 6 12 70.S70.s 77,4 fi 2 tq.a _zi,l I 0 33 9 -0.3 6 695 691 I \2{ 2a.o2a,o 3.23,2 tz z -tzl.i 2 7_,7 rrs.stts.s 116.2t16,2 3 0r ,.i:2o.3 I 4 479 893 2 9* 21.r21,1 2a.4 rzl.gtzl.g : :: 9: 3 4 3t0 -23\ 6' 218 218 -rnnn r 13 r4 21 28.s ta.t -160 e ,aoF 48.0 ;3- 5 4 lot3 -980 6* 239 3 r3r l?? j I 1',331t:i; ;i3i 3li ;:i -299 er 23r 136 266 s8o I ?rs -6e3 ;X ;;; 1 41 190 17? 6' 262 -lI3-:1" 3 i. ::3; :3: 8 9 a24 a26 5 13* 274.,- 3r Jr 1647ro4/ 1640rb40 lt 0 ga2 I 6" 2a6 -75 ' -.t ,"0fi ,,1, ,u,26j ,ru136 l1 o 982 994 4 1404 1395 10 91 2o 5 -ai 7 L!. 28 5 -30 i 5 l. 25.0 1I 4 -397 L2;; 1' 247 2ai 234 7 tt2 2t2 t2 9. 28s 4s 2 \4 4?a '465 7 3 s!.i -ssi 2 | 766 7so l3 4' 263 15 7 32a7 \ I 2o33 2oe22Og2 4 I 144?84 _795-7ss 3339 I ro r8r.r -188.7 ll\ e 3* 22.e -166 8 2O33 l5 4* 249 39 7 1394 1 il. i'"i 30.7 3 3 73.2 -84o 6 I 29.4 332 t389 3 lO* 22.6 33s ll 31 25.1 14.2 7 1568 266 -225 1542 5 t331u.s a.i 7 1095 I084 ::'::.:'lt:! L=s ::"'i:i':i: '3i 3i:3 ii.i 706 7!A e09 2 4 eso -e3o 12 710 -682 7* 25J -243 ::" :t: e 6* 26s _28e L, 2?a rs8 rO* 26S _46 I 0 t44 -9r8 q q iO:,r rOo.O'i;3 -144 71 28! -418 rr E* 283 -19 -167.2 I48 9 I 'i 10'Lo. 28zat 3 '-36-zeoO 3 o lr8oll3 0 -lls6-ll5 6 6 4.4* ,o.a2O,S 4j.3 | 2 r6a.2 203 lt7 3 487 426 2 302 840 8* 204 s6, -:,1.1 357 4 r1 !8.? ; 3" Lt ;9', ,2 2. 1i| 1?I i 3-'ll,ii:i ,ill i 3- tri.j 71S 621 ar 2ta -226 .litr ii: iii -l:i;.; ; 3 1:3 lti,"iZ rz:i t.1: za:22d it2:2 i I 3. i li31 ,'" ;: 1\tr 8* 235 -A2 ;ii ll 0 8o.o -84.6 I er ji.l -44.0 9 2' 24.9 29.4 27 247 8 ii:.':, i;i:l: -15.y-' ,i 3 I:"."" I i: z6.s _lli tr: t:,e )9.1 81 254 366 11: l2'- 13 0 dl 8 -408 I s 44o 39.8 n s* 2a.2 18.4 rr 2 7r.7 6?.J tt5 tl8 3 l0 11* 283 250 3 5 \1g.3 _t22,7 a* 275 88 -120-3 72 73,3 12* 246 222 2 I 856 -796 S s 4A.7 SS.t I lO. 24,2 40.3 2 3 120,6 136 4 3 135 0 9* 205 2A4 12* 251 -'439 4 I 297 3lO 7 \ e7.7 \O0,4 3 Lo* 241 2a1 56,3 561 83 ?6T 91 2lt -291 12 608 -65s 6 lr 18s -t8 s s* :r.g _rg.e s ror 2ss 16l j -80 I ?!9 9!.1 a2 2 9 71 5 623 va 27o -5.2 8 lr 207 -16l rr s. ,o,o -ii,e ? lo 980 -988 8 3 496 -502 t20 Il5 4 9 792 199 L2' 2as -s1 l0 rr 230 -266 rz s* zaz z7i s lor 282 -396 19 l: '-9\ 31 -541 12 I _394 ,2 3* 282 2?O 7* 25O 9 609 463 - 14? 26.I Jo.t ,;; ;; ; 2 6 46.0 4a.4 2 rl 1o.7 -73.3 7i 9 116 9 -116 5 -6 19.0 102 26,7 34,8 4 6' 20.5 ,18.9 4 ltr 26.1 30.4 L 1' 20 9 4 7* ,6,8 -2aL 25O LO. 22 a -28 a 276 234 | t 535 660 6e 6o 1103rros -ll0,l-rlo,i 6 l1 lll6 ll96 3 4' 2L4 7 1634 160 2 tor 22 8 -30 I 28.9 9.9 r 2 lo2.s -9s.6 8 6. 23.s -t.a 8 II s4.l s?.4 s 4' 22.4 -La-6 7 900 -91 6 10, 239 r2s.4 s 2 4a.7 43.7 o, l9 r2s.o lg 6 7s 3 7s.o I tz* 26.s -34.8 Z 1:2 I!.1 r0 5 L0. 254 _4sr 7 z" re8 2S 276 2s4 rz o. zta zt.i i' i;: ;::; il:; .1: :il ::1 -16 ro' 272 77 e2920 o -es-953 3 s9 2' z2.o -36.s " rr 4 62.4 -s6.7 I 135 9 -.oi,g l1 -40.9 L 7 198 23 5 5 l2i ;].2 i;.; 8 550 495 oa.o 2 42.6 ,.:r" 11' 23 I 92 13 2" 26 t t -;;.;zss.e _zst.i-;;:i a 2L4 -11 6 -634 a 42 1 | \?. ?9i -3Bs?1.? 41 s2. so7 sol!1! ll 664 L-4 ^^ a ; 2 13'- :l:27a :-1 a 242 ,36 I 11 41r 386 2 3 226 -sB ; ; .;ii 4 B' 2a3 -M4 6 s ?ro -747 -29 il.i a" 243 5 tt' 257 tt6 7326 -.7449 4 3* \74 2t6 I 7 6n7 _57.4 I 14 762 -759 d s' 25L -262 a' 263 19 5 -27 -J54 l0 s \tr 27,3 4 966 9Sr 6 3 392 rL 7" 2jL \\.2 737 774 -72 JO98 l2lO 8 3 588 -529 CRYSTAL STRUCTURE OF TETRAGONAL LEUCITE lll

T.csr-nl, Continued

ool !. Fol F. Fo r'. h k E. h k 1r"l lr" lr" lr" lr" lr" h k h k h k ]o.i 263 -15 I 257 128 51 239 l9 r 2 325 I 6 r432 1 I 860 90t 9* 269 r5 9 -32 261 51 245 -00 2. 269 555 609 3 6 209 I t* 257 9r 278 -3E 8 5 408 -41 2 10 2. 246 26s -r2l 5 6. 263 II L* 276 -337 9 iI3 9 109 0 ,5:0 -43 a7 21 a 50 530 249 91 279 3 s" 269 3+ 240 6a 2 2 479 610 268 545 la+ 26 7 t47 s 635 57 1 I 491 9 6" 265 392 5 53 520 21 5 -31 I 2. 222 t0* 21 3 34 -180 1t 6 793 -396 6 67 1 -67 4 3* 252 253 ?86 -44 2* 234 l0* 28 2 286 -s83 6* 211 t03 3" 264 26 I 62 2 7. 23.2 8 2 500 269 45 598 6 559 475 31 219 273 J7 7. 238 10 2* 267 r72 rt* 21 6 r50 -23 -62 r 287 196 249 t2 2. 2E7 332 \r* 27 9 6 6 680 7* -21 283 tt+ 2a 7 09 6' 282 I 25r E 7 374 774 4* 584 332 1 3 14t \2+ 2A 7 -41 3 -537 lc 7. 280 -2s3 7 499 -56 s 4 928 259 93 0 -93 l 3 3* 227 -! 1* 25A -19 E 26 9 2 24 1 -32 9 8. 23E 5 3 864 1003 t = ll -243 7 ta24 10I 4 988 935 8' 243 7 3' 244 5* 248 278 -22 A -941 0 634 7* 240 253 8* 251 9 3 954 I 7a3 149 283 1S 0 42 1 E 8r3 11 3+ 279 193 3 8 1269 -123 8 51 260 259 J09 283 +40 8 49 I 5 o 727 497 5* 272 ,51 2 1* 222 8l 8 502 286 r 7 0r 249 8* 269 45 5 5* 286 27 I 17 3 9' 249 4' 229 -334 9 0 640 688 255 4a 241 174 8 809 6 938 261 -351 !=15 9* l1 0 67 I -84 t4E 9* 267 -497 9* 265 8 4' 256 6 64 I 535 0* 272 178 -28r 2 L' 225 9* 273 t0 8 9' 278 !0 4* 273 6* 271 276 227 276 -r37 9. 242 33 I a* l0* 25 7 t* 232 1t4 -7\1 -199 I 5* 250 -160 0* 283 I0* 26 t t* 243 279 269 4 8 -511 3 s 2324 2391 to* 27 5 7* 260 I 581 10. 26 9 E I 389 75 2 7l 9 5 5 397 405 I0' 27 9 03 1* 26 4 r, 2ao 36 28 0 l0 t* 275 ,29 4 287 -ltl l0* 7 5* 2s2 -366 l0* 28 6 7* 272 1* 288 213 2 649 lt 53 4 609 2 tr' 26 9 9 5* 250 263 I 7' 243 21 3 ll 6 2t 27 4 5l,r rt a14 ll 5 500 476 3 2* 229 27a 99 8* 269 2' ?7A 461 Ltr 2E 4 5 2' 239 2a7 392 -79 2 6* 234 -231 a, 215 2" 285 t2* 27 a 7 2 803 -50 865 894 I 6" 24\ -ss 0* 234 8 1029 3* 278 345 3 t2* 2A 2 9 2" 261 112 249 -594 6* :5,1 19 0 0 91 0 950 9+ 276 3 735 ll 2 785 0* 243 11 I 281 225 I 6* ?6s 130 9' 279 4 626 -55r !=10 -58 2 3* 229 0 635 -6E s l0 6* 2A2 9* 286 4' 283 249 3 91 5 o. 267 285 L0 617 2 0 43 0 7 798 -857 5* 285 02 3' 247 0* 284 43 6 26 1 79 0. 220 ?* 246 390 6 743 709 8 3 L2,13 r = l5 261 161 6 0* 232 7* 252 -343 1* 23 5 83 I 0 465 10 3* 279 354 ?J6 106 7* 264 L91 t* 240 o* 247 3l l0 o* 265 -t0 7 289 -155 1 649 617 t 4 849 t* 248 0* 251 -21 8 -267 2E6 o* 2a4 12 0" J 4 280 t s46 559 259 400 0 -105 7 8* 239 465 0* I08 0 641 -598 5 4' 245 Lr 27,6 t3 o* 271 18 3 939 l0l4 I | 2rs2 8* 256 406 l* 285 -39 7 4r 258 605 6l I 116 725 3 I 2045 81 265 -306 2a 238 21 7 0 l+ 289 312 9 4* 273 283 -554 -154 5 I 1849 6* 278 -198 2 1006 t02 1 2* 288 3 644 573

Tlnr-B 2. Final Atomic Coordinates,Anisotropic Temperature Factors (x l(})

R R A Atom sH(n') Brr R-22 R-33 "12 -13 '23

-1 -1 -2 (r) r(1) o.0s79(1) 0.3964(1) 0.1666(r) 0. 90 1s(r) 1o(1) 13(1) (1) (1) 0,0878(2) n z2< 0.1622(2) 2.7 -2(7) -1 (1) (1) r(2) 0.1676(1) 0.6115(1) 0.1283(1) 0.89 72(7) 14(1) 11(1) 3 0.1622 0.s878 0.125 -2(r) r(3) o.3924(1) o.6418(1) o.0860(r) o.9l 13(1) 16(1) L2(1) 1(1) o(1) n 22 F 0.6622 0.0878 -7{.3) o(1) 0.1318(4) 0.3131(4) 0.1100(4) 2.37 42(4) 25(3) 33(3) o(3) 6(') 0.1322(10) 0.2800(7 ) 0.1033(10) ?? -12 o(2) 0.0921(4) o.5107(3) o. r3o3(4) 2,32 3e(3) 24(3) 36(3) (3) 1(3) 2(3) 0.L467 0.4740 0,1778 -6(3) -r(2) o(3) 0.14s3(4) o.67 98 (4) o.227 s (3) r.82 33(3) 3o(3) 15(3) o(2) 0.1033 0.6322 0.2200 (2) o(4) 0.1333(4) 0.6841(4) o.o3s4(3) 1.88 29(3) 33(3) 18(3) 15(3) 5(2) 7 a.6467 0.0340 0.1178 -s o(s) o.29oo(3) o.s772(3) o.12Os(4) 1,99 23(3) 2s(3) 3s(3) 7(2) (3) 2(3) 0.2804 0.60s3 0.1322 -7 o(6) 0.4826(3) o.617 4(4) o. 1667(3) r.87 27(3) 26(3) 26(3) (2) o(2) s(3) 0.4700 0.6178 0.7467 -6(r) -rs K 0.3660(2) o.3645 (2) o.rr47(2) 4.2r 3e(1) 46(r) 90(2) o(1) (1) 0.375 0.375 0.125 15.4

For conparison, atomic parameters of cubic leucite (Peacot', 1968) are written in italics below each (1959) ' corresponding t"trrgon.i position. Bg-values are equivalent temperature factors attet Hatnilton Trs host 0.68 Si and 0.32 A1. K hosts 0.94 K, 0.05 Na and O.O1 Ca. Standard deviations are indicated in parentheses in terms of last significant figures. -u28r, -t20, -zhkgrz -2h1g13 -zkrg.,) The anisorropic remperarure facror has rhe form: erp (-tr2Brr l2 MAZZI, GALLI, AND GOTTARDI

TlsLr 3. Dimensionsand Orientationsof ThermalElliosoids

Alom u^a u^b u^c u^a u^b u^c H. *;. lH. u^a u^b u^c

r(1) o.09(1) (9) loo 1s9 (9) 1o8 (9) 0.11(1) 22(so) 1os(17) 74(s4) o.12(1) 70(s6) 76(18) 156(37) r(2) o.09(1) 72(22) 48 (7) 133(1s) 0.10(1) 29(16) 86(r7) 62(19) o.12(1) 69 (8) 138 (7) r24 (7) r(3) 0.10(1) (4s) 9s r22(r3) 148 (9) o.11(1) rr(24) ror(27) 89(4o) o.12(1) 1o0(13) 146(1o) 58(1o) 0(1) 0.13(1) (8) 82 1s0(10) 118 (9) 0.18(1) r27(7s) 117(10) 49(r4) 0.20(1) L42(Ls) 79 (9) 126(13) o(2) o.12(1) (s) 119 1so (s) 83 (7) 0.19(1) 88(2s) 83(16) 7(10) o.20(1) ls1 (5) 61 (6) 92(29) 0(3) 0.12(1) (11) (r4) e2 e7 173(16) o.1s(1) s4(13) 37(13) 97(77) 0.18(1) 143(13) s4(13) 92 (8) 0(4) 0.11(1) (33) s7 r32(r2) s9(47) o.r2(1) r24(32) 80(34) 36(43) o.21(1) r29 (s) 136 (4) 107 (5) o(5) o.12(1) (8) 139 s2 (9) 1o3 (6) 0.16(1) s5(10) 38 (9) 77(16) o. 19( 1) 72(rL) 87(r4) 162(13) 0(6) 0.13(1) r24(72) 136 (8) 66

Principal vibrations (rootnean-square) are in A; angles between crystallographic axes (a, b, c) and principal axes (U) of vibration ellipsoids are in degrees. slandard deviations are indicated in pareniheses in terms of the last sienificant figures. the existenceof merohedric twinning, which would lowing step the solution of the system: superimposethe hkl diffraction of the first individual with that for khl of the second,and vice-versa.The lo.szr3o"@*/)""""+ o.l8F:b"(kht)".,.: F:b"ekt) relative weight percent of the two individuals was [o.ttrio"(mD"".,+ 0.82F:b"@ht).o,,: F:b"(kht) calculatedas follows: 20 diffractions featuring rele- - vant lFone F""r"l differenceswere selected. Let us call gave Fobs(hkl)"o,,and Fob"(khl)"o,,which were used in - x the fraction of the first individual, Il x] being the further stepsof structure refinement. fraction of the secondone: x was calculatedso as to Two more least-squarescycles with anisotropic minimize the sum temperaturefactors yieldedR : 0.046 using the 5l I - observed reflections. | 1F"o""1hkt) lxF.,4'@kl) + [l - x]F",r",(khl)ll Refinement including all reflec- tions convergedin the samenumber of cyclesto R : This minimum was obtainedwith x : 0.82.In the fol- 0.152. The assignment of different proportions

Tlst-r 4. Interatomic Distancesand Ansles

T(1)-tetrahedron - T ( 2) te trahedron T (3 ) -tetrahedron K-polyhedron .te r(1 r)-o(1 r) r.6s2(6); r)-o(2 r) 1.648(5)i r(3 r)-o(3rv) 1.644(s); K(r)-o(1 r) 3.138(7); -o(1 rr) 1.637(6) -o(3 r) 1.6s7(s) -o(s -o(2 -o(2 r) 1,.654(6) vr) 3.035(7) r) 1.540(5) -0(4 I) r.653(5) -0(6 r) 1.6s1(s) -0 (3vrr) -o(4rrr) (s) -o(s 2.986(7) 1.64s r) 1.668(s) -0(6 v) r.676(5) -0(4vrr) 2.966(6) -o(5 r) 2.9s6(7) mean L543 mean 1 .656 mean 1.655 -0(6 IV) 3.oo4(7) mean 3.014 o(1 r)-o(1 rr) 2.736(8) o(2r)-o(3 r) (7) -o(2 2.677 o(3rv)-o(5r) 2,7L0(7) K(r)-o(1rrr) 3.s06(7) r) 2.652(8) -o(4 r) 2.672(7) -0(6 r) 2.698(7) -o(3 -o(4rr1) -o(s rv) 3.759(7) 2.12r(7) r) 2.736(8) -0(6 v) 2.1os(7) -o(3 vr) 3.724(7) o(1rr)-o(2 r) 2,644(8) o(3 r)-o(4 r) 2.646(7) 0(s r)-0(6 r) 2.6s2(7) -o(4 -o(4rrr) -o(5 vr) 3.634(7) 2,617(7) r) 2.748(7) -0(6 v) 2.728(8) -o(s (7) 0(2 r)-o(4rrr) rv) 3.617 2.129(7) o(4 r)-o(5 r) 2.74s(7) 0(6 r)-0(6 v) 2.728(8) -0(6 r) 3.7rr.0) nean 3 .659 o(1 r)-r(1 r)-o(1 rr) 1r2,6(3)" o(2r)-r(2 r)-0(3 r) -o(2 108.2(3)" 0(3rv)-T(31)-o(s r) r10.s(3)" r(1 r)-0(1 r)-r(1 vr) r44.3(3)" r) 1o7.4 (3) -o(4 r) 1o8.1 (3) -o(6 r) r09.9(3) -o(2 r)-r(2 r) -o(4rrr) -o(5 154,0(4) 111.2(3) r) 111.2(3) -0(6 v) 109.1(2) r(2 r)-o(3 r)-T(3rrr) 129.7(3) o(1rr)-r(1 r)-o(2 r) 107.6(3) o(3 r)-r(2 r)-o(4 r) -0(4 -o(4rrr) 106,2(2) 0(s r)-r(3 r)-o(6 r) 106.7(2) r)-r(1 rv) 140.8(3) 10s.7(3) -o(5 r) 11r.5(3) -0(6 v) 110.5(2) -o(5 r)-r(3 r) 0(2 r)-r(1 r)-o(4rrr) 131.2(3) r12.3(3) o(4 r)-r(2 r)-o(s r) 111.s(3) o(6 r)-r(3 r)-o(6 v) 110.1(3) r(3 r)-0(6 r)-r(3vrr) 130.4(3)

Roman nuEerals refer to the follouing positions: I x y z III 3/4-y l/4+x t/4+z \t 3/4+y-I I/A-x+t t/4-z VII 1/4-y+I I/4+x 1/4-z II 7/4-y I/4+x t/4-z Iv 3/4+y-l 3/4-x 3/4+z_I vI 3/4+y-l l/4-x 7/4-z Standard deviations are indicated in parentheses in tems of last significanr figures. CRYSTAL STRUCTURE OF TETRAGONAL LEUCITE I l3 relating the two individuals of the twin did not yield (Peacor,1968); for the descriptionof this framework better R values. see Taylor (1930). No (Si,Al) ordering has been The observedand calculatedstructure factors are detected,as foreseenby Peacor(1968) on the basisof compared in Table 1. Final atomic parametersand the rapidity of the high-low inversion. The average anisotropicthermal parametersare given in Table 2. T(2)-O and Z(3)-O distancesare in perfect agree- Table 3 gives the thermal ellipsoid data. Bond dis- ment with the expectedvalue (1.656A) accordingto tancesand anglesare listed in Table 4. Jones (1968) for Al:(Si+Al) : 0.32. The average A comparison of the final atomic parameterswith Z(l)-O distanceof 1.634A (0.013shorter) would be those deduced from the cubic structure adapted to proper for Al:(Si+Al) 0.25. None of the the tetragonal system (Table 2), or with those framework atoms shows a marked anisotropic ther- proposed by Wyart (1940), shows differenceslarger mal vibration. The kind of displacementsthe than I A. ttrls explains the failure of least-squares framework undergoeswhen changingfrom the cubic refinementusing theseas starting coordinates. to the tetragonalstructure is shown in Figure l. The changespertain mainly to the shapeof the cavitiesoc- Discussionof the structure cupied by K atoms. To explain this point, let us con- The tetrahedralframework of tetragonalleucite is sider the averageK-O distancesin feldspars,which topologically identical to that of the cubic phase range from 2.93 to 3.00 A. The averagevalue for l2-

______l -U8 114? I \ 0t|'1285 |

--Il8- o(l)1lo

t's( 0(5'r)-129 -.:

P{ K272

odlo23 0tf fr )215 -o-----3/0 ol6ho? ^118

0 012^

Frc. l. The lower part (from z = 0 to z = l/4) of the unit cetl of leucite projected along c. Both the tetragonaland the cubic structuresare shown.The tetragonalis shown as full lines,and the positionsof the correspondingatoms are given in Roman letters(K, T, O) and three digit numberswhich give the heightover the projectionplane as permillageof c. The cubic framework is shown as dashedllnes, and the positionsof the correspondingatoms aregiven in italic letters(K, I' no letterfor oxygens)and numberswith the samemeaning as before The symmetry elementsand the dotted lines(K-O bonds) refer to the tetragonalstructure The origin of the cubic cell is shiftedby a/2 with respect to the tetragonal cell. n4 MAZZI, GALLI, AND GOTTARDI

Tlst-r 5. SomeBond Distancesin Mineralswith the LeuciteFramework.

Expected bond Six shortest distances Mrneral Average of the six shortest distances distances in the cubic structure in the non-cubic structure

Leucite K-0 2.eB ; (1) 3.35A (Peacor,1968) 3,0I A (this work) -0 Ana 1c ime o (H20) 2.60-3.o4(2) 3,4r (Fernaris et aL,,1972) PolIucite Cs-0 3.26 (1) 3.39 (Beger,1969)

(1) Highest possible average values (I2-fo1d coordination) (Shnnnon and PreDitL, 1969) (2) Hmilton and rbers. 1968

coordination is 2.98 A ltable 5). In cubic leucite concerningthese two mineralsand iso-structuralpol- (Peacor,1968) each K atom is coordinated to 12 ox- lucite. A first glanceallows us to concludethat in the ygens,with 6 oxygensat 3.35A and 6 at 3.54A; these cubic structuresthe cavity is too largefor K and HrO, are proper values at high temperature, where the but not for Cs; thus at lower temperature a tetragonal cubic phase is stable, but they are high for room structure is more stablewhen the cavity is occupied temperature. In tetragonal leucite the K cavity is by K (leucite)or by HrO (analcime),but no evidence compressed,so that eachatom is coordinatedto 6 ox- has been given so far of the existenceof a non-cubic ygensat -3.0 A, with 6 other oxygensat 3.5 to 3.8A. structure for pollucite, Cs[AlSLOo], and in our opin- The latter distancesare too long to be considered ion the cubic phase is the only one possiblefor this bond distances.The thermal vibrations of the K compound. atoms are remarkably anisotropic. Acknowledgments Possible implications for structures This researchwas made possiblethrough financial support ofthe with leucite framework Consiglio Nazionale delle Ricerche, Roma. Analcime, which is isostructuralwith leucite,also References exhibits a polymorphic inversion from a high- (1969) temperature form with spacegroup la3d to a low- Becen, R. M. The crystalstructure and chemicalcomposi- tion of pollucite. Z. Kristallogr. 129, 280-302. temperatureform of unknown (see, symmetry for in- BustNc, W. R., K. O. MenrrN, lNo H. A. Levv (1962)Onrls, a stance, Coombs, 1955). The change of lattice Fortran crystallographic least-squaresrefinement program. U.S. parametersis lessmarked than in leucite,but in the Natl. Tech. Inform. Seru. OnNI--rrra-305. powder pattern somepeak-broadening occurs and, in Coours, D. S. (1955) X-ray observationon wairakite and non- one case, peak-splitting. At least four lines are pres- cubic analcime. Mineral Mag. 30,699-708. DAvrEs, J. E., nNo B. M. GArEHousr (1973) The crystal and ent which do not conform to the condition "hhl: 2h : molecular structure of unsolvated p-Oxo-bis-[N,N'-etbyle- 1- I 4n" ofthe spacegroup la3d. Their spacingsare nebis(salicylaldiminato) iron (lll)1. A cta C rystallogr. E.29, 1934- 6.88,3.24, 2.36, and2.29 A. The first wasindexed as t942. 200 by Coombs (1955),the secondis either 4lt or Frusr, G T. (1963)Phase transition in syntheticand natural 330, the third is 530 or 433, the fourth is 600 or 442. leucite. Schweiz. Mineral. Petogr. Milt. 43, 165-195. Frnnnnrs, G., D. W. JoNrs, ero J. Yeurss (1972) A neu- Reflections200, 4l I, 433,600, and 442 are all com- tron-diffraction study of the crystal structure of analcime, patible with the spacegroup of low-leuciteI4r/a, and NaAlSirO5. H2O. Z Kristallogr. 135, 240-252. so we may advance the hypothesis that the low- Grnvntr, G., P. MnrN, nNo M. M. WooLFsoN(1971) The applica- temperaturesymmetry is the samefor both analcime tjon of phase relationships to complex structures, III. The op- and leucite,and that the cubic structur€ is displaced timum use of phase relationships. Acta Crystallogr. A27, 368-376. in the same way for both minerals during the high- HlvrLroN, W. C. (1959) On the isotropic temperature factor low inversion. On the other hand the chemical equivalent to a given anisotropic temperature factor. Acta analogy is not as strong because,in analcime,water C rystallogr. 12. 609-610. moleculesoccupy the equivalentK sitesof leuciteand -, and J. A. Ibers (1968'l Hydrogen Bonding in Solids. W A. Na enters sitesthat are vacant in leucite. Benjamin, Inc., New York. Henson, H. P., F. Hrnueu, J. D. Lae, lNo S. SrllueNrl (1964) With the aim of giving a better explanationof the Hrs atomic scattering facttrs. Acta Crystallogr. 11, 1040-1M4. similaritiesbetween the high-low inversionsof leucite JoNrs, J. B. (1968) Al-O and Si-O tetrahedral distancesin alumi- and analcime,we havecollected some data in Table 5 nosilicate framework structures.lcrd Crystallogr. 824, 355-358. CRYSTAL STRACTURE OF TETRAGONAL LEUCITE lt5

Konernwn, M. (1969)Uber die Verzwilligungdes Leucits.Z. TAyLoR,W. H. (1930)Thestructureofanalcite(NaAlSirOG'HrO). Kristallogr. 129, 34f-350. Z. Kristallogr 74, l-19 NAnav-Szrn6,Vor.r, S. (19a2)Die Strukturdes Leucits KAlSirO'. WYART,M. J. (1938)Etude sur la leucite.Bull. Soc.franc. Minbral. Z. Kristallogr 104, 39-44. Cristallogr. 61,228-238. PEAcoR,D. R. (1968)A high temperaturesingle crystal diffrac- - (1940) Etude cristallographiqued'une leuciteartificielle. tometer study of leucite, (K,Na)AlSi?O0. Z. Kristallogr. Structure atomique et symatrie du min€ral. Bull. Soc. franc. 127,213-224. Minbral Cristallogr63' 5-17. S,coeNecA..R.. AND T. Ozrwa (1968) Thermal transition of letcite. Mineral.J 5,321-333. SunNNoN,R. D., et.loC. T. Pnswrrr (1969)Effective ionic radii in Manuscriptreceiued, March 3l , 1975;accepted oxidesand fluorides.Acta Crystallogr.Bi25,925-946. for publication,July 24, 1975.