American Mineralogisl, Volume 66, pages 410-423, l98I

Natroapophyllite,a new orthorhombic sodiumanalog of apophyllite I. Description,occurrence, and nomenclature

HtRou.lnu MATSUEDA Institute of Mining Geology Akita University, Akita 010,

YesuNoRr Mrun-e.' eNo JoHN RucrrDce Department of Geology, University of Toronto Toronto, Ontario MsS IAI, Canada

Abstract

Natroapophyllite NaCaoSirO2oF' 8H2O, a sodium analogof apophyllite,has beenfound in white skarn at the SampoMine, Okayama,Japan. Electron microprobe analysisof the min- eralgives SiO252.79, CaO25.4l, NarO 3.05,K2O 0.33,F 2.27,HrO (by difference)l7.ll weight percent;(-O=F' : 0.96).Optical and crystallographicparameters are: a: 1.536(2),B : 1.538(2),y: l.5tA(2),2V(meas.):32(l)",r

Introduction and Rucklidge, 1979).The Na-rich examplesare in- The nomenclatureof the apophyllite group is com- variably orthorhombic and fluorine-rich, and the proposed plex. Fluorapophyllite and hydroxyapophyllite have name natroapophyllitehas been for this so- recently been defined by Dunn et al. (1978) as the dium analog of the orthorhombic apophyllite de- valid names for the end members of the tetragonal scribed originally by Sahama (1965) and Belsare apophyllite series,in which K is the major alkali cat- (1969).It is not the sodium analog of ordinary tetra- given ion. Orthorhombic varietiesof apophyllite have also gonal apophyllite. The name natroapophyllite, been described.Sahama (1965) gave details of an or- in allusion to its compositionalrelation to apophyl- thorhombic fluorine-rich apophyllite KCa.AlSi, lite, was approvedby the IMA Commissionon New 1976. OroF'8HrO, which containedsignificant Al. and New Names in October, prefixes would Although Na may substitute for K in apophyllite Other additional for natroapophyllite to a small degree,samples in which Na predominates be in order, e.9.,ortho- and fluor-, but in the absence over K have only recentlybeen described (Matsueda, of non-orthorhombicor other than fluorine-rich nat- 1975,1980; Miura et al., 1916;Miura, 1977;Miva roapophyllite, it seemsunnecessary to burden the lit- erature with more complex names than natroapo- phyllite, orthorhombic I On leavefrom Departmentof MineralogicalSciences and Ge- which is defined as being the ology, Faculty of Science,Yamaguchi University, Yamaguchi753' sodium end member of the apophyllite group miner- Japan. als with the formula NaCaoSi'OroF'8HrO. 0003-004x/8I /030+04 l 0$02.00 410 MATSUEDA ET AL.: NATROAPOPHYLLITE

Fig' l. Optical micrographsof natroapophyllitefrom the Sampo Mine. (a) Compositecrystals of typical natroapophyllite(SA-lb) and fluorapophyllite(SA-la). SA-l samplesare up to 0.15 x I mm. (b) Compositenatro- (SA-2a)fluorapophyllite (SA-2b) crystalsand intermediatecompositions (SA-2c, d, e).

Sampledescriptions, physical properties, and generationby the granite intrusion (Matsueda,1980). morphology The white skarn was formed by fluorine metasoma- tism of ferrobustamite and wollastonite-andradite The four samplesdescribed here have SA-numbers skarns (Matsueda, 1980). In transmitted light the referring to the Sampo Mine, some l0 km west of grains of natroapophyllite are invariably rimmed by Takahashi City in Okayama Prefecture.The Sampo apophyllite (Fig. l), which suggeststhat a pseudo Mine is one of the typical contact metasomaticore solid solution exists between apophyllite and nat- deposits of the Chuhgoku Province and was em- roapophyllite, in which there is a transition from te- placed at the contactof Paleozoiclimestone and slate tragonal to orthorhombic symmetry.This would rep- with Late Cretaceousgranite (Matsueda, 1973, 1980). resent a range of chemical variation beyond the Natroapophyllite occursin associationwith zeophyl- solid-solution series fluorapophyllite to hydroxy- lite, cuspidine,apophyllite, and calcite in the 'hrhite apophyllite reportedby Dunn et al. (1978)and Dunn skarn" on the 9th level, No. I Yoshiki Ore Body of and Wilson (1978). the mine. Other associatedminerals include andra- Natroapophyllite samplesSA-l to 3 in Table I oc- dite, xonotlite, wollastonite, a clinopyroxene in the cur as minute prismatic euhedral to subhedral crys- diopside-hedenbergiteseries, magnetite, quartz, and tals up to 0.15x I mm (Figs.I and2), brownish-yel- native bismuth, all of which occur in banded zones low to yellowish-brown (in SA-l and 3) or colorless betweenthe granite and marble contacts.Natroapo- to white (in SA-2). The luster is vitreousto pearly. A phyllite was found in the white skarns close to the typical exampleof natroapophyllitein SA-l is zoned marble contact(Matsueda, 1973, 1980). The fluorine- with fluorapophyllite, and the two phases are re- bearing silicates zeophyllite and apophyllite crystal- ferred to in Table I as SA-lb and SA-la, respec- lized during a hydrothermal alteration stage,which tively. Compositecrystals exhibit {100} prisms trun- occurred after the thermal metamorphism and skarn cated by the {l I l} dipyramid striated perpendicular 4t2 MATSUEDA ET AL: NATROAPOPHYLLITE

Table l. Occurrences,parag€nes€s, compositions, and optie axial anglesof fluorapophyllite and natroapophyllite from the Sampo Mine

SpeciEen No. Occurrence Paragenesis Alkalj- contenE* 2V(neas.)

Kt SA- la Whlte skarn Zeophyllite, calcite, . o8Nto.ozc"4. t3 '1 I SA- Ib (9L No.1 Yoshiki ore Body) andradite, f luorite, cuspidine Ko.o6Nto.9oc"4.13

Ko -?l SA-2a .03*"0. 86c"4. 08 Kr >>0 SA-2b . olNto.02c"4 . 09 Druse in white skarn llagnetite, andradite, SA-2c Ko. >0 (9L No.1 Yoshiki Ore Body) fluorite 4oN"o.z8ct4 . oo 1 SA-2d Ko.85Nto. roca4. 16 Kt SA-2e . ogN"o.o3c"4. ol Ko. =30 SA-3a o7N"o.75c'4. r2 White skarn Fluorite, xonotolite, SA-3b Ko.45Nuo.5lct4. 1 (9L West No,I Yoshiki Ore andradite, magnetite, cuspidlne l2 SA-3c Body) *o.95Nto.03c"4. zo j.n >0 sA-4 Spherical skarn marble t3 (10L l{rest. No.l Yoshiki Fluorite, andradite "o.9oNto.o3ct4. Ore Body)

* Atonic z'atios of aLkali ions on the basis of Si = 8.00. to the c axis (Fig. la). SpecimenSA-2 is subdivided to that offluorapophyllite (Figs. I andz) because,as 2a-2e for varying compositionsin the rangenatro- to shown below, the crystals are compositeswith the fluorapophyllite.It exhibits well-developedfl I U di- rims being K-rich fluorapophyllite and the cores Na- pyramids with {100} prisms which give the samplea rich natroapophyllite.Optical measurementcould be "fish-eye" appearance(Figs. lb and2\. The external morphology of the crystalsis sinilar

'fish Fig. 2. Scanningelectron micrographs of natroapophyllite(SA-2a). (a) Subhedralcrystals of SA-2 showing eye' appearance.(b) Euhedral crytsalsof SA-2. MATSUEDA ET AL.: NATROAPOPHYLLITE

%.\ Oo(41) @ o(41)o

ox) si (1) Qc'rzl

,a Ca(l) .J O o(41)OI !"-els'

Fig. 3. The Si6O2ssheet in natroapophylliteprojected on (001).

mademost reliably on specfunenSA-l in which the K amountsof calcite and fluorite is 2.50,and the calcu- and Na phasesare easily distinguished. The Na-rich lated value is 2.30. Natroapophyllite is slightly sol- component is colorless in thin section and distinctly uble in l: I HCI and 1: I HNO3. biaxial with 2V(meas.): 3211;o,r 1 via : 1.536(2), B : 1.538(2)and y : 1.54r'r(2\.The K-rich com- Chemistry ponent is uniaxid with the propertiesof normal fluor- The chemical compositions of the natroapophyllite apophyllite, ar : 1.536and e : 1.539(see Table l). and fluorapophyllite crystals were determined with Biaxial examples of the K-rich component are also the JXA-5A electron microprobe analyzer at Kytrshtr noted in Table l, but the detaileddescription of these University. The analyses, which were performed at phaseswill be reservedfor a separatepaper. l5kV acceleratingvoltage and l5nA samplecurrent, Cleavageis perfect on {001} and poor on [ll0]. are shown in Table 2, along with a list of the stan- The Mohs hardnessis 4 to 5, and the is light dards used.Water was determinedby difference.No gray. The mineral does not fluoresce in UV radia- other elements besides those listed were detected in tion. An IR spectrumof natroapophylliteis shown in either form of apophyllite from the Sampo.Mine. Part IL The powder usedfor this was carefully sepa- Wet-chemical analysis of somewhat impure material rated from the K-rich fluorapophyllite parts of the including a small amount of apophyllite from the crystals. The spectrum shows two sharp peaks at same locality was performed by Dr. K. Ishibashi of 3560 and 3420 cm-' and one broad peak at 3020 Fukuoka University, using weight loss on ignition. cm-'. Thesecorrespond to two strong and one weak The resultsare HrO(+) : 15.83and HrO(-) : 0.14 hydrogen bonds (see Part II). The specific gravity, weight percent.An analysisof the most Na-rich spec- measuredby the suspensionmethod in Thoulet's so- imen (SA-lb) with 3.05 weight percent NarO is pre- lution on somewhatimpure materialsinsluding small sented in Table 2. We define this as the type compo- 414 MATSUEDA ET AL; NATROAPOPHYLLITE

Table 2. Microprobe analysesof fluorapophyllite and natroapophyllite

SA-la SA-2b SA-2c SA-2e SA-3a SA-3b SA-1c SA-4 SA-lb NatroapophyLlite* **SA-2aNatroapophyllite ***** **** (I{t.Z) (Atonlc Ratio) (wr.Z) (Atontc lratlo) (wt.U) (wt.Z) (wt.z) (wr.z) (llr.z) (wr.U) (wr.Z) (I.lt.U)

slo2 52.79 s1 8.00 51.46 Si 8,00 51,61 5L.26 52.67 52.Lr 51.85 52.08 52.O9 5L,66 Al2O3 0.00 Al 0.oo 0.00 A1 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Fe2p3 Fe 0.02 Fe 0.002 0.01 0.00 0.01 0.05 0,o2 0.01 0.03 CaO 25.4L Ca 4.L3 25.43 ca 4.08 24.84 24.49 24.6L 24.39 24.90 25.06 25,54 24.90 Mso Mg 0.00 Mg 0.00 0.02 0.04 0.01 llno l4n 0.00 lh 0.00 0.00 0.04 0.05 Na2O 3.05 Na 0.90 2.95 Na 0.85 0.08 0.20 0.96 0.11 2.50 1.7r 0.26 0.09 K2o 0.33 K 0.05 0.18 K 0.03 5.47 5.06 2.08 5.58 0.38 2.29 4.84 4.56 E 2.27 F 1.09 2.25 F r.06 2.32 2.6L 2.54 2.40 2.72 2.64 2.83 2.5L Itzo(+) (I7.1r) o 29.88 (16.66) o 28.67 (16.65) (17.44) (18,13) (16.35) (18.75) (17,31) (r5.62) (17.31) Total I00.96 100.95 100.98 101.10 101.07 101.01 101.15 101.11 101.19 10r.05 0=F" 0.96 0.95 0.98 1.10 1 07 1.01 1,15 1.11 1.19 1.06 (100.00) (100.00) (100.00) (100.00) (100.00) (100.00) (r00.00) (100.00) (10o.oo) (100.00)

1 0n the baeie of Si -- 8.00. ** Standrcds wed i.n tlp electm mi.crcprcbe aalyeee m syntletic CaSi?3(fon Ca and Si.); AL2og(AL); ag?(Mg); oatyzed lurcttte(Fe); nwryorceite(I,ld; albite fzon AreLia(Nd; orbloclase(D; od f'Lrcrtte(F).

sition for natroapophyllite, for which the formula is: K-rich fluorapophyllite, and the inner regiorxi are Na-rich natroapophyllite. (Nao.rolQ.*)o.ruCao.,Si, 8.6HrO r *F,.o"Or0..' The analysis of the intermediate zone in SA-2 is on the basisof Si : 8.00.Type material of natroapo- deficient in alkalis, and the nissing cations may be phy[ite SA-3, which resemblesthe SA-l specimen,is Li* or HrO*, neither of which can be measuredby deposited in the National Science Museum, Shin- electron probe microanalysis. juku, Tokyo and Institute sf I\4ining Geology, Min- These data support the proposition that natroapo- ing College, Akita University, Akita. phyllite is chemically an orthorhombic sodium The composition of uniaxial (or biaxial, seeTable equivalent of fluorapophyllite. l) K-rich apophyllite, which usually rims the nat- X-ray crystallography roapophyllite, was also determined by electron mi- croprobe analysis and is shown in Table 2. The unit-cell dinensions refined from 15 reflec- Chemical 2sning can be seen in the microprobe tions collected with a Syntex PT automated single- analysesof Table 2. In the caseof SA-l only the Na crystal diffractometer, from a single crystal of nat- and K extremesare seen,and the zoning is discontin- roapophyllite(SA-1), are a:8.875(4), b : 8.881(6), uous, somet:mesoscillating. SpecimensSA-2 and c : 15.79(l)A;V: 1236.943andZ: 2' The space SA-3 show intermediate compositions as well, and group was assignedas Pnnm or Pnn2 on the basis of from this evidence we propose the existence of a Weissenberg film data. The unit-cell dimensions of solid-solution series. However, there are optical dis- the SA-la specimenare distinctly larger than those continuities in these two samples, with the light re- of typical natroapophyllite (SA-lb) becauseof the gions being Na-rich and the dark K-rich (see Fig. partial K substitution for Na. lb). It is difficult to establishthe preciseoptical prop- X-ray powder di-ffractometer data for natroapo- erties of the parts of the crystals with intermediate phyllite SA-lb are given in Table 3, wherethe values compositions. Therefore it is not clear at what com- of dcalc. and hkl were obtained from the computer position the orthorhombic-tetragonal transition oc- program of Appleman and Evans (1973). Spurious curs or whether gaps exist in the solid-solution series. lines attributed to minor amountsof fluorite and zeo- Some of 1ls ssning has the appearanceof composi- phyllite have been omitted. 1trs lsp4ining lines, tional change taking place during growth (SA-l), which do not show clearly the splitting which would while in SA-2 the 2ening appearsmore characteristic be required by orthorhombic symmetry, are pre- of alteration. However, in general the outer zone is sentedas single values, llus 6aking the pattern in- MATSUEDA ET AL.: NATROAPOPHYLLITE 4t5

Table 3. X-ray powder diffraction data for natroapophyllite (SA- cessof dobs. over dcalc. suggeststhat some of the K- lb); fluorapophyllite (SA-la) impurities may have been included rich fluorapophyllite has been included in the pow- in the sample material der along with natroapophyllite.

h.kL d- r- d.hkt d. r- carc oDs obs carc oDs 06 ril (A) t,&l (;') Discussion

7.89 002 7.83 20 2.545 132 z'oo I Analogous to the alkali feldspars,where the degree 7,74 101,011 7.71 18 2.642 3r2 I 6.28 r10 6.28 4 2.476 133 of substitution of Na and K varies with temperature r r

II. CrystalStructure

YesuNoRt Mlune2 Department of Geology, University of Toronto Toronto, Ontario M5S IAl, Canada

Tosulo Kero Institute of Earth Sciences Yamaguchi University, Yamaguchi 753, fapan

JOHN RUCKLIDGE Department of Geologt, University of Toronto Toronto,O4tario MsS IAl, Canada

AND HIROHARU MATSUEDA Institute of Mining Geology Akita University,Akita 010,Japan

Introduction Experimentalmethods and results The chemical and crystallographicdata presented A crystal 0.2 x 0.3 x 0.3 mm was mounted on a in Part I suggestthat fluorapophyllite and natroapo- Syntex PT automated single-crystal ditrractometer phyllite are isostructural. Crystal structures of tetrag- equipped with a graphite monochromator, at KyUshtr onal potassium-richfluorapophyllite have been de- University. MoKa radiation was usedto measure984 tennined by Taylor and Ndray-Szab6 (1931), and crystallographically-independent reflections up to 20 refined by Colville et al. (1971),Chao (1971),Prince : 60o,of which 563 reflectionswere judged to be sig- (1971),and Bartl and Pfeifer (1976);and that ofte- nificant (I -- 3). No absorption corrections were tragonal potassium-rich hydroxyapophyllite by made, since the size and nature of the crystal was Rouse et al. (1978). Crystal structures of ortho- small enough for the effect to be negligible. The unit rhombic potassium-richapophyllite (Sahama, 1965; cell parametersd : 8.875(4),D : 8.881(6),c : Belsare, 1969),however, have not been determined 15.79(l)A, V: 1263.9L'wererefined fron tle data becausethey are complexlytwinnsd. It is well known for the 15 strong reflectionsused to orient the crystal that minor amounts of Na replace K in apophyllite, on the SyntexPl. but no reportson the crystal structureof natural nat- The crystal was from the Sampo Mine and was roapophyllite with Na/K >> I have been published. designatedSA-lb. This was the most Na-rich among In this section the results of a crystal structure the specirnensfound there (Tables I and 2). Ten analysisof natroapophyllite (SA-lb) are given. The other specimenslisted in Table I contain less Na, differential thermal analysis (DTA), thermogravi- and are intermediate in composition between fluor- metric analysis (TGA) and IR absorption spectrum apophyllite and natroapophyllite. The specimen of the new mineral are also reported. Comparisons which gave the sharpest reflections on Weissenberg are made with tetragonalapophyllites of other work- photographswas SA-2, which originated in a druse ers. According to the redefinitions of Dunn et al. in the white skarn. SA-l and SA-3 specimens,on the 'fluorapophyllite.' (1978)we refer to the latter as other hand, yielded slightly di-ffusespots, but showed more Na enrichment than SA-2. Figure 1(a) shows an optical nicrograph of SA-1, where zoning due to can be seen.The crystal (SA-lb) 2 On leave from Department of Mineralogical Sciences and Na-K substitution Geology, Faculty of Science,Yamaguchi University, Yamaguchi from SA-1 used for the structure determination was 753, Japan. selectedbecause it had the smallestcell parametersof MATSUEDA ET AL.: NATROAPOPHYLLITE 417

the six measured,and hencethe highest Na content. Table 4. Atomic coordinates and isotropic temperatur€ factors of Althougb it appeared to be optically homogeneous natroapophyllite(SA- I b) when placed in an oil cell in the spindle stage of a polarizing microscope,we cannot excludethe possi- Atom bility that submicroscopicK-rich regions exist, and sr(1) o. zzSg(:)* 0.0833(3) 0.1890(3) 1.12 (6) these might account for the diffusenessof the reflec- si(2) 0.4161(3) 0.2708(3) 0.3108(3) 1.13 (5) tions. The compositionassumed for this crystal (SA- ca(1) 0.1143(3) o.246s(3) 0 1.20 (6) lb) was that of the most Na-rich analysisfound in ca(z) 0.7s37(3) 0.1148(3) o 1.2s (6) SA-l (seeSA-lb in Table 2). Na0 0 z 2.84(20' Starting parametersof the ions and water mole- FO 0 o r.87 (24) cules in natroapophyllite were taken from the refine- o(1) o.3677(7) 0.1322(8) 0.2513(6) 1.36(13) (8) ments of the fluorapophyllite structureby Colville et o(2) 0.0882(7) 0,1902 o.2L62(6) 1.63(15) o(21) 0.3099(8) 0.4123(8) 0.2839(5) 1.59(14) al. (1971) and Chao (1971). Their parameterswere o(3) 0.2696(8) 0.098 7 (8) 0.0921(6) 1.7s(15) modified appropriately to account for Na sub- o(31) 0.4016(8) 0.2305(8) o,4079(6) L.66(74) stituting for K and the reduced symmetry (ortho- o(4) 0.2286(9) o.4s0s(9) 0.0887(6) 2.45(r8) rhombic yr. tetragonal),which for most atoms causes o(41) o.s5o2(9) 0.2253(11)0.0890(7) 2.,70(19) a doubling of the number of independentatomic po- n(1) 0.47(1) 0.17 (1) 0.0s(1) 1.6 sitions in an asymmetricunit. Hence Si(l) and Si(2) H(11) 0.17(1) 0.s4 (1) 0.08(1) L.4 were derived from Si, O(2) and O(21) from O(2) and H(2) 0.16(r) 0.43 (1) 0.14(1) 0.8 (1) so on. Atom O(l), however,does not split. The O(l) H(2r) o.56<2) 0.31(2) o,14 3.2 site in the tetragonalcell lies on a two-fold axis at z : { and has a multiplicity of 8. In the orthorhombic cell this site becomesa general position, again with a multiplicity of 8, but z is no longer constrainedto the enceof a centerof symmetryis also supportedby the value {. fact that refinement converged in space gtotp Pnnm The refinement was carried out with the full-ma- to give an unweighted final residual of 0.056 com- trix least-squaresprogram FLS4 written by Sakurai pared with 0.3 when spacegroup Pnn2wastried. The (1967).'Neutral atom scatteringfactors for Na, Ca, final atomic parameterswith their standard devia- Si, F, and O weretaken from the International Tables tions are given in Table 4. The calculatedinteratomic for X-ray CrystallographyVoL IV (1979; the 0.33 distancesand angleswith errors are listed in Table 5. weight percent K indicated by the electron micro- Natroapophyllite is built of sheetsof four-mem- probe analysis(Table l) was neglected.The recipro- bered rings of alternating tetrahedra (Fig. 3) with in- cal variances,l/d, of the structure-factoramplitudes terleaving sheetscontaining the Ca and Na atoms. were used as weights in the refinement, except for Natroapophyllite is essentiallyisostructural with unobserved reflections which were assigned zero apophyllite (Taylor and N6ray-Szab6,l93l) and hy- weight. A three-dimensionaldifference Fourier syn- droxyapophyllite (Rouse et al., 1978),with Na sub- thesiswas made and the possiblepositions of hydro- stituted for K and the ion pairs Si, Ca, O(2), O(3), gen atomsH(l), H(ll), H(2), and H(21) were found O(4) having two independent sets of coordinates in the map. However, the isotropic temperaturefac- (Table 4) becauseof the lowering of symmetry from tor of hydrogen atom H(21) was rather large (about tetragonalto orthorhombic. 3), and hence this position is less well determined than the others. Si-O tetrahedra The assignmentof the spacegroup of natroapo- The tetrahedra formed around the two Si atoms phyllite to Pnnm was based on the results of running have slightly different configurations.The Si(l) ions the data through the center of symmetry detection are coordinatedto O(1), O(2), O(21), and O(3). The program Rsws3 written by Sakurai (1967).The pres- Si(2) ions are coordinated to O(l), O(2), O(21) and O(31) (Figs.4 and 5). Figure 6 shows the Si(l)- and Si(2)-tetrahedra 3 To obtain a copy of a list of the observed and calculated forming rings of four Si tetrahedra around the two- structure-factoramplitudes, order documentAM-81-154 from the fold axis. Eight-membered rings of tetrahedra are Business Office, Mineralogical Society of America, 2000 Florida Ave., N.W., Washington, D.C. 20009.Please remit $1.00 in also located in this plane, thus forming a layered advance for the microfiche. structure parallel to the perfect {001} (Fig. 418 MATSUEDA ET AL.: NATROAPOPHYLLITE

Table 5. Bond lenglhs and bond anglesin natroapophyllite(SA-lb)

tond lengths (i)

SiO4 Tetrahedtg Tetrahedra (O-O) Ca(O,F)7Polyhedra si(1) -o(1) 1'.631(8) o(1) -o(2) 2.s89(9) ca(1)-o(3) 2.396(8) -o(2) L.626(7) -o (21) 2. s68(10) -o(31) 2.392(8) -o(21.) 1.616( 7) -o(3) 2.675(L2) -o(4) 2.49r(9) -o(3) 1.578(10) o(2) -o(21) 2.629(Lo) rr€Eln 2.426 mean 1. 6l_3 -o(3) 2.662(17) o(21)-o(3) 2.660(r_1) ca(2)-o(3) 2.399(11) sl(2) -o(1) 1.608(8) mean 2.63L -o(31) 2.213(8) -o(2) 7.624(7) -o(41) 2.490(10) -o(2r_) L.627(7) o(1) -o(2) 2.569(10) mean 2.367 -o( 3r_) 1.s 79 (9) -o(21) 2.s90(10) mean 1.610 -o(31) 2.64o(L2) ca(l)-F 2.473(3) o(2) -o(21) 2.632(10) ca(2)-F 2.412(3) Si-Si -o(31) 2.660(11) o(21)-o(3r.) 2.665(11) I12OMol-ecules si(1).-s1(2) 3.038(s) meao 2.626 s1(1)--si(2) 3.064(4) H(r) -o(3) 2.0(1) -o(41) 1.1(1) NaOgPolyhedron H(11)-o(3r-) 1.8(1) Na-o(4) 2.763(9) -o(4) 1.0(1) -o(41) 2.8s4(10) rr(2) -o(21) 2.6(L) o(4)-o(41) 3.487(L2) -o(4) 1.0(1) rr(21)-o(2) 2.3(r) -o(4r_) r-.1(1) Bond Angles (degrees) Tetrahedra (O-S1-O) Tetrahedra (Si-O-Si) o(1) -si(1)-o(2) 10s.3(4) o(11)-sl(2) -o(2) 10s.3(4) sl (1)-o (1)-si (r_) -o(21) 104.s(4) -o (21) 106.4(4) 139.4(5) -o(3) LL2.9(4) -o(31) 11r..8 (4) si (r-)-o (2)-si (2) o(2) -si(1)-o(21) 108.4(4) o(2) -sl(2)-o(21) 108.2 (4) r41.6 (6) -o(3) Lrz.4(4) -o(31) Lr2.3(4) si(1) -o(2r)-si (2) o(21)-sr(1)-o(3) 112.8(4) o(21)-s1 (2) -o(31) Lr2.4(4) r41.3(6)

t ?he syrtnetz,y tzwtsfonn is gLoen ae foLlous: t+c, t-A, i-2.

o(3)

si(2)o !sitrl

o( 1)

Si( 1)-tetrahedron Si( 2)-tetrahedron

Fig. 4. Geometry of O-O distancesof Si(l)- and Si(2)-tetrahedrain natroapophyllite. MATSUEDA ET AL.: NATROAPOPHYLLITE 4t9

o(31) phyllite, both in the Si(l) and the Si(2) tetrahedra, but the bond angles O(l)-Si(2FO(21) and O(l)- S(2)-O(31) ditrer significantly from those of fluo- rapophyllite. The S(l)-O(2)-Si(2) bond angles, l4l.l' and l4l.3o, are slightly larger than those of fluorapophyllite, 140.8o(Colville et al., l97l; Chao, l97l;Bartl and Pfeifer, 1976). Figure 3 showsthe SirOrosheet of natroapophyllite (SA-lb) projectedon (001). The Si-O tetrahedraare slightly deformed by the shift of the atomic positions of O(l) and O(21), which have such a large effect on the distorted ring of four Si-O tetrahedra ortho- rhomic symmetry results. The displacement which largely affects the change of symmetry from tetrag-

A=1O5.3 A'=1o5. 3 B=108.2 B' =108.4 C=1r2 4 C' =112 .8 D=111.8 D' =112.9 ll= 106 . 4 E'=1O4.5 F=112 3 F' =rl2 .4

Fig. 5. Bond lengths in A and bond angles in degreesof ttre Si(l)- and Si(2)-tetrahedraprojected on (010).

3). Note the similarity of the apophyllite structure in this projection to that of sanidinewhen projected on the (201) plane (Ribbe, 1975).However, in apophyl- lite each of the tetrahedra in a four-membered ring points the sameway, while in sanidinethe two pairs comprising the ring point up and down, respectively. In the tetrahedrallayer, O(l) is sharedbetween the Si(l)- and the Si(2)+etrahedrawhich point upward @@o@@ and downward along the c axis. On the other hand, O(2) and O(21) are sharedbetween Si(l)- and Si(2)- tetrahedra, which surround the Na atom and point in the same direction. Only the unshared oxygens, O(3) and O(31), are bonded to the interlayer Ca(l) and Ca(2) atoms (Figs. 6 and 7). The Si(l)-tetrahedra have bond lengths which are longer to O(l) and shorter to O(3) and O(21) than those of fluorapophyllite. The mean distanc€s of Si(1)-tetrahedra of natroapophyllite, however, are similar to those of tetragonalapophyllites (Table 6). On the other hand, the Si(2) tetrahedra are dis- torted on account of O(l), O(31), and O(2), which are shifted significantly when compared with the ox- ygens of the Si(l) tetrahedra. The mean Si-O dis- tance in the S(2) tetrahedrais l.610A, which corre- sponds to the minimum value of the grand mean Si- @Ooo o O bond length in silicate structures (Brown and Ca(1) Na O(4) F si(t) si(2) Gibbs, 1969).Figure 5 and Table 5 show that mean Ca(2) o(41) bond anglesO-Si-O are similar to thoseof fluorapo- Fig. 6. The structur€ ofnatroapophyllite projected on (100). MATSUEDA ET AL.: NATROAPOPHYLLITE

o(3)

H(11 Ca(1) rr(2)cati

o(41) H(2x) '.utrl I

Ca(2)

o(31)

2) o("l: 31 11)

O..QH. oSlii@8lil,oF oH

Fig. 7. The Na, and Ca(l) and Ca(2) sheetin natroapophylliteprojected on (001).The probable positionsofhydrogen atoms H(l), H(ll), H(2), and H(21) are also shown. onal to orthorhombic is not so marked in the Si te- Na-O polyhedra trahedra as it is in the Na-O(a) bond lengths and The Na atoms, whose ionic radii are less than O(41) positionsas discussedbelow. those of K, replace the K atoms of apophyllite. In Ca-O polyhedra fact, the Na-O(4) or Na-O(41) bond lengths, 2.763 or 2.8254, respectively,are shorter by about 5 per- Figure 7 showsthe Na and sheets Ca in natroapo- cent on average than those of fluorapophyllite, as phyllite projected on (001). The Ca(l) and Ca(2) listed in Table 6. The smaller cell dimensions of nat- atoms are bonded to O(4) and O(41), respectively, of roapophyllite (SA-lb) are thus mainly due to the the water molecules.These oxygensare shared with substitution of Na for K. This substitution also re- the Na atoms.The Ca(l) and Ca(2) are also bonded sults in lowering the symmetry from tetragonal to or- to four oxygensO(3) and O(31), and to the F atom. thorhombic. The mean Ca-O distance is similar to that in fluo- rapophyllite (Tables 5 and 6), but Ca(2)-O is signifi- HrO molecales cantly shorter, especiallyfor Ca(2)-O(31). The dis- tance of O(3) or O(31) betweenthe upper and lower In the final difference Fourier map, rather diffuse Si-O tetrahedra is 2.909A, which is slightly shorter peaks were evident, which were taken to indicate the than in fluorapophyllite, 2.911to 2.9194 (Colville er possiblepresence of the hydrogenatoms H(l), H(l l), al., l97 l; Chao, l97 l; Prince,l97l). H(2), and HQD; but the atoms H(3) and H(31), cor- MATSUEDA ET AL.: NATROAPOPHYLLITE 421

Table 6. Selected meatr interatomic distances (A) of natroapophyllite (SA-lb) compared with those in the apophyllites previously reported

Natroapophyllite CoLvILLe et aL. Chao Prince Bartl and Pfeifer Rouse et aL. (sA-3) (1e71) (1e71) (1e7r-) (Le76) (1978)

sl-o t.613 1.610 1.516 L.6L4 1.615 1.615 1.616 Ca-O 2.426 2.367 2.427 2.422 2.430 2.422 2.43s Ca - F,OH 2.413 2.4L2 2.4L6 2.478 2.429 2.4r4 2.435 Na,K - O 2.763 2.8s4 2.972 2.97L 2.950 2.965 2.9s4 o(4) - o(4r_) 3.487 3.690 3.694 3.672 Tetrahedra (o-o) 2.63L 2.626 2.636 2.632 2.637 - L.772 n(1) o(3) 2.O 1.8 L.827 L.762 j z.tt+l - o(4) 1.0 1.1 0.968 0.983 0. 983 H(2) - o(2) 2.3 2.6 2.693 2.269 2.250 ) r.srz - o(4) 1.0 1.1 o.5s2 0.958 0.953 respondingto the H(3) reportedby Prince (1971)and DTA and TGA curves Bartl and Pfeifer (1976), could not be found in the Diferential thermal analysis of natroapophyllite expectedpositions. Tables 5 and 6 show that the H- (Fig. 8), heatedin air at the rate of l2"C/min, shows O bond lengths are similar to those of fluorapophyl- two main endothermicpeaks at 380oand 460oC.The lite. But the relaxation allowed by the orthorhombic peak at 460"C is broader, with two barely distin- symmetry results in slight changes in the geometry guishable maxima at 455" and 468oC (Table 7). o(3)-H(l)-o(41)-H(21)-o(2) and o(3I)-H(l 1)- With the exception of the doubling of the second O(4)-H(21) con-figurations,which would be identical peak, the curve is similar to those reported for fluo- in the caseof tetragonalsymms1ry. The anglesH(l)- rapophyllite by Colville et al. (1971), Chao (1971), O(41)-H(21)and H(ll)-O(4)-H(2) are lll(7)' and and Bartl and Pfeifer (1976).The sameinterpretation 94(9)", respectively; the angles O(2)-H(21)-O(41) given for apophyllite is applicableto the DTA curve and O(21)-HQ)-O(4) are 137(ll)o and 176(9)';and for this specimen;namely, the first and secondbroad the anglesO(3)-H(IFO(41) and O(3l)-H(l 1)-o(4) peaks occurring at the different stagesmay be due to arc 124(9)0and 157(l l)'. That thesedifferences may lossof HrO and HF, respectively.The latter molecule be significant is supported by the independent DTA may be formed at higher temperature, as pointed out and IR data discussedbelow. by Colville et al. (1971),Chao (1971),Prince (1971) and Bartl and Pfeifer (1976). Thermal gravimetric analysis, run in air at a heat- ing rate of 6"C/min, showsthat water loss starts at about l60oC and continuesuntil a discontinuity be- tween4l0o and 500"C, as shownin Figure 8. The de- hydration is more rapid until it reaches16 percent to-

> tal weight loss at 700oC,which is similar to that of fluorapophyllite (Colviile et al., l97l; Chao, l97l; Bartl and Pfeifer, 1976).

F 6 =U IR spectrum Figure 9 shows the OH stretching vibration and absorbedwater regions of the IR spectrum of nat- roapophyllite (SA-lb). The spectrum shows two Fig. 8. Differential thermal and gravimetric analysis curves for sharp absorptionbands at 3560 and3420cm-', and a natroapophyllite (SA-lb) from the Sampo Mine. broad band at about 3020 cm-'. MATSUEDA ET AL.: NATROAPOPHYLLITE

Table 7. Endothennic peaks,dehydration and IR absorption bands ofnatroapophyllite (SA-lb) and the apophyllites previously reported

Speclnens Endotherolc peaks ("C) Dehydration (oC) Absorptloo bands (ln cn-l) (mA dara) (TGA date) (IR data)

Kanioka apophyllite 334 280 (Koizuni,1953) 440 280-440 Phoenix apophylllte 3560(sharp) 225-600 (Colwtlle et aL., 325 3070(broad) L97L) 450 Mont. St. Hilalre 350 apophylllte 375 250 (Chao,1971) 458 Ceatervllle apophyllite (Prlnce, 1971) Apophylllte 320 200-320 (Bsrtl and Pfeifer, 350 320-580 L976) 450 SaEpo 380 3560(sharp) natroapophyllite 455 160-500 3420(sharp) (in this study) 468 3020(broad)

Discussion The latter two, being the longer, are therefore the An extension of the interpretation given by Col- weaker and account for the two sharp absorption ville et al. (1971) for fluorapophyllite can be applied bands at 3560 and 3420 cm-'. the former two are to the IR data. They concluded that their sharp ab- shorter but give broad absorption bands which over- sorption band at 3560 cm-' indicated a weak hydro- lap and are not resolved in the spectrum. gen bond, while their broad band at3O7Ocm-' meant The doubling of the sharp band in the 3500 cm-' a stronger one. In our spectnrm,two sharp absorp- region is a direct consequenceof the orthorhombic provides tion bands occur in the 3500 cm-' region, which sug- symmetry, and satisfying confirmation that gests that there are two weaker hydrogen bonds of the data from independent methods are consistent slightly di:fferentstrengths. Q6alfining the results of with each other. It also suggestsa rapid method for the IR data and the crystal structure analysis leads to testing for orthorhombic symmetry in the apophyllite the conclusion that there are three (and possibly group. As mentioned above,the DTA curve showsa four) different structural environments for the hydro- brsad endothermic peak with two maxima at 455" gen atoms in the water molecules.Table 5 shows that and 468oC.1tris dsuUing, which is not seenin any the bondsH(l)-O(3), H(ll)-O(31), H(2)-O(21),and of the curves reported for tetragonal apophyllites, H(21)-O(2) are 2.0, 1.8,2.6, and 2.3A respectively. could conceivably also arise from the lowered sym- metry. However, it would be unwise to place too much weight on theserather tenuousdata. The crystal structure of natroapophyllite is iso- structural with that of fluorapophyllite, with allow- ance made for the reduction in symmetry from

o tetragonal to orthorhombic. In order to establish where the symmetry change takes place in the K-Na series, and how much solid solution ex- a substitution ists, systematic structure determinations and IR measurementsof other samples with compositions intermediate between fluorapophyllite and 1600 1500 natroapophyllite are required. In view of the diffuse- trave nubcr ( o-1; nessof the reflections from the most Na-rich crystals, Fig. 9. IR absorption spectrum for natroapophy[ite (SA-lb) high-resolution transmission electron microscopy from the Sampo Mine. may be informative. MATSUEDA ET AL: NATROAPOPHYLLITE 423

Acknowledgments Matsueda, H. (1973) On the mode of occurrence and mineral paragenesisof iron-wollastonite (ferro-bustemite) skarn in the National We thank Dr. A. Kato of the Scicnce Museum, Japan Sampo Mine, Okayama Prefecture (in Japanese).Science Re- for valuable suggestionsregarding the naming of this new mineral; ports, Departmentof Geology,Kyusht University, 11,265-273. White, Museum Dr. J. S. National of Natural History, Smithso- Matsueda, H. (1975) "Na-apophyllite" from the skarn of the dan Institutioq lv6shingto4 D.C. for valuablediscussions; Dr. T. Sampo Mine, Okayama Prefecture, Japan (abstract, in J.apa- Watenabe of KyDshD for his help in DTA, University the TGA nese). Annual Joint Meeting of JapaneseAssociation of Miner- and IR measurements. alogists, Petrologists, and Economic Geologists; Mineralogical The calculations were carried out on the FAcoM M-200 at the Society of Japan; and Mining Geology. Abstracts with Program Computer Center of Kyushu University and also on the HITAc (Kofu),7s. 880Ocomputer at T6kyo University. Y. Miura acknowledgesa fel- Matsueda,H. (1980)Pyrometasomatic iron-copper ore depositsof National lowship from the Sciencesand Engineering Research the Sampo Mine, Okayama Prefecture. Part I. Geology and which work was Council of Canada under this completed. Mineralogy. Journal of Mining College, Akita University, Se- Drs. R. C. Ewing and P. Dunn are thanked for their critical ries A, 5(4), 15-77. manuscript. conrments on the Miura, Y. (1977) Cation distribution and physical properties in apophyllite-type structure (abstract"in Japanese).Annual Meet- References ing of JapaneseCrystallographic Society. Abstracts with Pro- Appleman, D. E. and Evans, H. T. Jr. (1973)Job 9214:Indexing gram, lB-3. and least-squaresrefinement of powder difraction data. U.S. Miura, Y. and J. C. Rucklidge (1979) Variations in apophyllite Dept. of CommerceTechnical Information Service,PB2l6, 188. structure and chemistry (abstract). American Crystallographic Bartl, H. and Pfeifer, G. (1976) Neutronenbeugungsanalysedes Association. Abstracts with Program (Honolulu), Series2, 6(2)' Apophyllit KCa4(Si4Oro)2(F/OH) . 8H2O. Neues Jahrbuch fiir 89. Mineralogie Monatshefte,58-65. Miura, Y., Matsueda, H. and T. Kato (1976) Crystal structure of Belsare, M. R. (1969) A chemical study of apophyllite from Na-substituted apophyllite from the Sampo Mine, Okayama Poona.Mineralogical Magazine,37, 288-289. (abstract, in Japanese).Annual Meeting of Mineralogical So- Brown, G. E. and Gibbs, G. V. (1969)Oxygen coordination and ciety of Japan. Abstracts with Program, 130. the Si-O bond. American Mheralogist,54, 1528-1539. Prince, E. (1971) Refinement of thc crystal structure of apophyl- Chao, G. Y. (1971)The refnement of the crystalstructure of apo- lite. III. Determination of the hydrogen positions by neutron phyllite. II. Determination of the hydrogen positions by X-ray difraction. Anerican Mineralogist, 56, 1243-1251. diffraction. American Mineralogist, 56, 123+1242. Ribbe, P. H. (1975)The chemistry,structure, and nomenclatureof Colville, A. A., Anderson,C. P., and Black, P. M. (1971) Rcfine- feldspars. In P. H. Ribb€, Ed., Feldspar Mineralogy. Mineralog- ment ofthe crystal structureofapophyllitc. I. X-ray diffraction ical Societyof America, Short CourseNotes 2, Rl-R52. and physical properties. American Mineralogist" 56, 1222-1233. Rouse, R. C., Peacor, D. R. and Dunn" P. J. (197E) Hydroxy- Dunn" P. J. and Wilsor; W. E. (1978)Nomenclature revisions in apophyllite, a new mineral, and a redefinition ofthc apophyllite the apophyllite group: hydroxyapophyllite, apophyllite, fluor- group. IL Crystal structure. American Mineralogist" 63, 199- apophyllite. Mineralogical Record, 3, 95-98. 202. Dunn, P. J., Rouse, R. C. and Norberg, J. A. (1978) Hydroxy- Sahama,Th. G. (1965) Yellow apophyllite from Korsnas, Finland. apophyllite, a new mineral, and a redefinition of the apophyllite Mineralogical Magazinc, 34, 406-415. group. L Description, occurrenc€sand nomcnclature. American Sakurai, T. (1965) Universal Crystallographic Computation Pro- Mineralogist,63, 196-199. gram System.Crystallogr. Soc. Japan, Tokyo. Koizumi, M. (1953)The differential thermal analysiscurves and Taylor, W. H. and N6ray-Szab6,St. (1931)The structureof apo- the dehydration curves ofzeolites. Mineralogical Journal, l, 36- phyllite. Zeitschrift fiir Kristallographie, 77, 146-158. 47. Kurokawa, K. (1967)Apophyllite found in the Kdmori Ultrabasic Mass (in Japanese).Journal of JapaneseAssociation of Miner- Manuscript received,October 15, 1979; alogists, Petrologiss, and Economic Geologists, 57(6), 232-237. acceptedfor publication, October 30, 1980.