Canadian Mineralogist Vol. 18, pp. 77-84 (1980)

TETRANATROLITEFROM MONT ST.HILAIRE,OUEBEG

T. T. CHBN* AND GEORGE Y. CHAO Departmentof Geology,Carleton University,Ottawa, Ontario KIS 586

AssrRlcr Sourvrerne 'onatrolite Tetranatrolite is a new name for "tetragonal Tetranatrolite est un synonyme de natrolite", a first reported from Ilimaussaq, t6tragonale", nom sous lequel un min6ral fut d6crit Greenland by Andersen et aI. (L969). It is a wide- par Anderson et al. (1969) qui l'avaient trouv6 i spread constituent in the pegmatitic dykes and Ilimaussaq (Gro6nland). Ce min6ral est un consti- miaroles in the syenite at Mont St-Hilaire, tuant trBs r6pandu dans les dykes pegmatitiques Qu6bec, occuritrg most commonly as epitactic over- et dans les cavit6s miarolitiques de la sy6nite er growths on natrolite and as small euhedral n6ph6line du mont St-Hilaire, dans la province de crystals or silky fibrous sprays on natrolite, anal- Qu6bec. Il se pr6sente le plus commun6ment sous cime or microcline. It occurs less commonly as forme d'enduits 6pitactiques sur cristaux de na$o- irregular earthy patches on natrolite or analcime. lite ou de petits cristaux idiomorphes ou encore The mineral is white, translucent to opaque with d'agr6gats de fibres soyeux sur natrolite, analcime vitreous to dull . The hardness could not be ou microcline. Moins souvent, on le trouve en determined, and was not observed. The taches terreuses irr6gulidres sur natrolite ou anal- mineral is readily soluble in 1: I HCL slowly in cime. C'est un min6ral blanc, translucide b opaque, 1:1 HNOg and is only slightly attacked by 1:1 d'6clat vitreux i terne, dont la duret6 n'a pu 6tre H2SO4. Optically the mineral is uniaxial positive, . d6termin6e et otr nul clivage n'a 6t6 d6ce16.Il est 1.481 and e 1.496. Single- photographs show facilement soluble dans 1:1 HCl, difficilement the mineral to be tetragonal, I42d or l41md,, a dans l:1 HNO' et d peine attaqu6 par 1:1 HrSOr. 13.098(2), c 6.635(2) A. Witn D*u 2,276 s/cm}, Optiquement, il est uniaxe positif, avec et 1.481 et a we find 2 - 4, whence Dcarc = 2.234 g/cmg. 1.496. I*s clich6s de_cristal unique r6vdlent sa Strongest lines in the powder X-ray-diffraction sym6trie t6tragonale, I42d ou l4rmd, a 13.098(2), pattern are 6.549(5 ) (2OO),5.9 12(4) ( l0 l ), 4.635 (4) c 6.635Q) A. Pour une densit6 mesur6e di, 2,276, (220), 4.387(5)(2rr), 4.r43(4)(310), 3.189(5) on trouve Z : 4, d'ot la densit6 calcul6e de 2.234, (32r), 2.867(10)(411),2.438(4)(43r); 1.816(4) Les raies les plus intenses du diagramme de poudre (640,413), 1.721(4)(730\. Electron-microprobe sont les suivantes:6.549(5)(200), 5.912(4)(101), analysis gave: SiO2 46.9, TiA2 0.06, Al,Os 25.6, 4.63s(4) (220), 4.387(s) (zrL\ , 4.143(4)(3LO) , CaO 1.48, MgO n.d., FeO 0.11, Na,O 14.0, K,O 3.189(5)(321), 2.867(10)(411), 2.438(4)(43r), 1.12, HzO+ (TGA to 1000"C), 9.59, H,O- (TGA 1.816(4) (640,413), 1.72L(4) (730). L'analyse i la to 135'C) 1.31, sum 100.18 (bv weieht). The microsonde 6lectronique donne: SiO, 46,9, TiOt analysis corresponds to (Nar.zsCoo.roKo.or)Feo.o,0.06, Al,O" 25.6, CaO 1.48, MgO n.d., FeO 0.11, Ai1.s5Si..n2O16.2.06HrOor, ideally, NarAlrSirOro' NagO 14.0,KrO 1.12,HrO+ (ATG jusqu'd 1000"C) 2HrO. A TGA curve shows a minor weight-loss 9.59,HrO (ATG jusquti 135o) 1.31,somme 100.18 between room temperature and 135"C and a major (en poids). Cette analyse donne la formule (Nar.r5 weight-loss between 135 and 435"C. The infrared Cao.roKo.os)Feo.orAlr.esSis.orO1o.2.06HrO ou id6ale- spectrum of the mineral strongly suggests (Si,Al) ment, NagAlgSLOm.2HrO. La courbe d'ATG mon- disorder. Hydrothermally the mineral decomposes tre une faible perte de poids entre la tempdrature to nepheline and analcine at 445oC and 1.0 kbar. ambiante et 135'C et une perte plus forte de 135 and to analcime at 330"C and 0.5 kbar. No change e 435'C. Le spectre infrarouge indique un d6sordre was observed at 265"C and 0.5 kbar. The mineral (Si,Al). La tdtranatrolite subit une d6composition is a dehydration product of a higher hydrate. hydrothermale en n6ph6line et analcime (445"C, 1.0 kbar), ou en analcime seulement (330'C, 0.5 Keywords: tetranatrolite, St-Hilaire, Qu6bec, natro- kbar); i 265'C et sous 0.5 kbar, on n'observe lite, pegmatite, epitactic overgrowth, Si,Al disorder, aucun changement. Ce min6ral provient de Ia . d6shydratation d'un hydrate sup6rieur. (Traduit par la R6daction)

*Present address: CANMET, 555 Booth Street, Mots-cl6s: t6tranatrolite, St-Hilaire, Qu6bec, natro- Ottawa,Ontario KIA OGl. Communicationsshould lite, pegmatite, enduit 6pitactigue, d6sordre, Si,Al, be addressedto GeorgeY. Chao. syenite n6ph6linique. 77 78 THE CANADIAN MINERALOGIST

INtnoouctloN is apparently affected by the humidity of the immediate environment. The well-defined boun- A tetragonal analogue of natrolite was first daries between the altered crust and the trans- found in the albitite veins cutting the naujaite parent core material are either smooth or inclusions in lujavrite in the westernmost part irregular surfaces, apparently without transi- of Tugtup Agtakorfia, Greenland, and was tional zones (Figs. l, 2). When the crust described by Andersen et al. (1969). The min- material is removed, the freshly exposed trans- eral was found as aggregatesof sheaf-like groups parent core material does not show sign of of small prismatic crystals, each of which dis- further alteration during a period of more than played a single prism and either a pinacoid or a year under similar conditions. The freshly a dipyramid. The mineral was reported as com- collected material may be preserved in water, monly associated with aegirine, analcime, na- but the altered crust material does not recover trolite, , epistolite, schizolite, lepidolite, its transparency after being immersed in water sphalerite and a number of beryllium . for several months. The X-ray powderdiffraction pattern of the Studies of this alteration material from Mont mineral was similar to that of natrolite but St"Hilaire by the present authors show that it could be indexed on the basis of a body-centred is a tetragonal dimorph of natrolite, similar in tetragonal cell with a 13.O43,c 6.619 A. fne compsition and physical properties to the optical properties of the mineral were also tetragonal natrolite from Greenland reported found to be consistent with those for a uniaxial by Andersen et aI. (1969). The name tetrana- mineral. Andersen et al. made no attempt to tolite was proposed for this mineral jointly by name this mineral at that time. the present authors with Dr. Andersen and his In studies of the minerals from Mont St- associates.The mineral and its name were ap- Hilaire, Qu6bec, it has been frequently noted proved by the Commission on . New Minerals that crystals of a variety of natrolite, usually and Mineral Names, I.M.A. Type specimens well formed and transparent when first col- from Mont St-Hilaire are preserved at the lected, alter after short exposureto air, produc- National Museum of Natural Sciences,Ottawa ing a white, translucent to opaque, friable and (37131) and at the Royal Ontario Museum, somewhat porous crust. The rate of alteration Toronto (M35545). A specimen of the mineral

Fro. 1. Tetranatrolite overgrowths on natrolite crystals (3 mm across) from Mont St-Hilaire. Frc. 2. Tetranatrolite overgrowth o! a tratrolite crystal with a portion of tetranatrolite removed, showing sbarp boundaries. Cross-sectionof crystal: 3 mm. TETRANATROLITE FROM MoNT sr-HrLArRE,eu6BEc 79

from llimaussaq, Greenland, an ideotype, is readily in 1:1 HCI and slowly iq 1:1 HNOa also deposited with the Royal Ontario Museum with gelatinous residues; it is only slightly at- (M36rcq. tacked by 1: I HzSO4. The optical properties of tetranatrolite and OccunnaNce AND PHySIcAL PnopsntrEs the associatednatrolite, summarized in Table 1, were obtained from crystal fragments previously Tetranatrolite is a widespread constituent in oriented by X-ray goniometry using a spindle the pegmatite dykes and miarolitic cavities in stage and light. All refractive-index the nepheline syenite at Mont St-Hilaire, and liquids used were checked using an Abb6 re- is closely associatedwith natrolite, microcline, fractometer. The maximum and minimum in- analcime, aegirine and a variety of accessory dices of refraction for tetranatrolite from Mont minerals. The mineral ocsurs most commonly St-Hilaire are slightly higher than those for the as a friable crust up to 1 mm thick on natrolite material from Greenland and are significantly crystals of various sizes (Fig. 1) and as small higher than those for natrolite from Mont St- euhedral crystals (0.1 mm) or fine, silky fibrous Hilaire and the Green River Formation, Colo- sprays on larger crystals of natrolite, analcime rado (Table 1). Composite tetranatrolite-na- and microcline. It occurs less commonly as trolite crystals show optical continuity in thin irregular, earthy patches on massive natrolite section, with the e direction of tetranatrolite and analcime. Tetranatrolite-coated natrolite parallel to the Z principal vibration direction crystals are very simple in habit, as is typical of natrolite, suggestingan epitactic relationship of natrolite crystals from this locality, display- between the two minerals. ing prism { I 10}, pyramid { I 11 }, with or without a small pinacoid {100}. Re-entrant angles in X.Rev Sruorrs the prismatic zone, indicating multiplicity of the underlying natrolite crystals, are very €ommon. Both the tetranatrolite crust and the asso- The mineral is white, translucent to opaque, ciated natrolite core were studied by X-ray with a vitreous to dull lustre. Owing to its diffraction, using Weissenberg, precession and peculiar mode of occurrence, the hardness of powder methods. From the diffraction symmetry the mineral could not be determined, and cleav- and systematic extinctions observed on single- age was not observed. Several determinations crystal photographs the space group for tetrana- of the density of the mineral by the flotation trolite was establishedto be I42d or l$tmd, thus metlrod gave 2.276(5) g/cm3, slightly higher confirming the space group I42d for the material than 2.254(5) g/c.m', the density of the closely from Greenland, deduced on the basis of syste' associatednatrolite, and 2.21O(2) g/cm", the matic extinctions in the indexed powd6rdif- density of tetranatrolite from Greenland (An- fraction data (Andersen et al, 1969). The sys- dersen et al. 1969). Tetranatrolite dissolves tematic extinctions observed for natrolite were

Tetranatrol I te Natr€l ite

Spacegroup rTzd 1T2d Fddz Fd& a (A) r 3.098(2) r3.047(2) r3.043(r) r8.308(7) r8.285(8) A 18.632(8) r8.636(8) c o. oJJ[2, 6.614(2) 6.6re(r ) 6.s89(3) 6.586(3) vot. (i3) 1138.28 2x1123,80 2x'l'122.12 z 4 4 !rorc 1.48r(t) r .480(l) r.478(r) r.4775(ro) 5 r.480(r) r.4810(ro) €orY r .496(r) I .4e3(l ) r.4e2(r) r.4895(ro) optic sign (+) (+) (+)2V-se' ooo. (s/crn3) 2.276(s) 2.2'to(2) 2.254(5) 2,25(r)

(l) Mont st-Hilaire, qudbec (this study). (2) Illmussaq, Greenland (thls study). (3) Ilfnnussaq, Greenland (Andersen etaL. 1959). Refractive indlces by double variatlon. (4) ltbnt St-Hllaire, Quebec(this study). (5) Green Riyer Fomation, Colorado (Pabst l97l). Refractiye lndJces for 589 un, 2fmeasured directly ln white llght. 80 THB CANADIAN MINERALOGIST

Frc. 3. C-axis Weissenberg photographs of (a) tetranatrolite, (b) natrolite, (c) twinned natrolite and (d) composite tetranatrolito-natrolite crystal. consistent with the space group Fdd2 assigned twin plane, or by [001] as the twin axis of 90" to natrolite by other authors (Meier 1960, rotation. Both types of twinning have been ob- Pabst 1971). Cell parameters for tetranatrolite served for natrolite from other localities (e.g. and natrolite from Mont St-Hilaire (Table l) IJey 1932, Pabst 1971). Theoretically, the two were obtained from single-crystal photographs types of twinning can be distinguishedby single- and refined by a least-squares method using crystal X-ray diffraction. Twinning by (110) powder-diffraction data. Single-crystal photo- as the twin plane brings a and b of one indivi- graphs were used as a guide for indexing. dual to coincide approximately (deviation 1') The single-crystal-diffraction photographs of with D and c of the other, whereas twinning tetranatrolite (Fig. 3a) are similar to those of by t001Jeo"produces exact coincidence of a and natrolite, which is orthohombic but pseudote- D of the two individuals. However, the poor tragonal in both cell geometry and X-ray dif- quality of the X-ray photographs of the twinned fraction intensities (Fig. 3b). The similarity is crystals from Mont St-Hilaire (Fig. 3c) does best shown by the Weissenbergphotograph (Fig. not permit an unequivocal determination of the 3d) of a composite tetranatrolite-natrolite twin law. Owing to the very small differense crystal fragment. In this photograph the epilactic between a all.d bo twinning by either twin law nature of the overgrowth of tetranatrolite on produces doubling of reflestions along the 20 natrolite is also evident. The single-crystal-X-ray axis as is shown in Figure 3c. The maximum reflections of tetranatrolite tend to be elongate splitting occurs along a* and 6* and minimum and somewhat diffuse; the diffuseness is more splitting along the row line IlOlE. The absence pronounced in the high 2d region. of the doubling of reflections in the photographs Twinning is very common in natrolite from of single crystals of ,tetranatrolite (Fig. 3a) Mont St-Hilaire, as suggested by the frequent eliminates the possibility that the tetragonal observationsof re-entrant angles on the crystals symmetry might be caused by twinning of or- (FiS. l). The twinning in the Mont St-Hilaire thorhombic natrolite. natrolite may be explained by (110) as the The X-ray powderdiffraction pattern of tetra- TETRANATROLITE FROM MONT ST-HILAIRE, QUEBEC 81

TABLE2. X-RAYPOI,IDER DIFFRACTION DATA FOR TEIRA{ATROLITE AND out the splitting of other less well resolved pairs TI,, MTROLITEFROM I4OI{T ST- HILAIRE.QUEBEC (Anderson et al, 1969, Plate 1).

t- I. w2 oDs oDs oo5 Cnervrrcer, CotvtposrtroN '10 200 6.549 6.549 6 Etn o.aal l0l 5.919 5.912 4 5.902 20 5.880 com- 4.660 Electron-microprobe analyses of eleven 220 4.631 4.635 4.612 4.579 posite tetranatrolite--natrolite grains were per- 211 4.391 4.3S7 4.377 l0 formed at 15 kV with a specimen current of 4. t50 pyroxene 310 4.142 4.143 4.104 about 50 nA. Standards used were 3,262 (for Ca, Si), jadeite (Na, Al), ilmenite (Fe, 3.194 6 l0 321 3.t52 Ti) and synthetic phlogopite K, Mg).The water 112 3.123 3.120 3.1t4 3.102 content was determined by TGA to 100O'C. The 5 202 2.959 2,960 2.949 2,940 averaged analyses (Table 3) may be recal- 420 2.929 2.926 2.914 I 2.899 culated, on the basis of 10 atoms per 20 2.862 411 2.865 2.867 l0 2.851 2.843 for.mula, to (Nar.zsCao.rolG.oe)F€o.orAl.grsis.osOro' 'I 2.O6H.2Ofor tetranatrolite and to (Nar.ooCao.or) 3"12 2.589 2.588 2.580 a.ata -(weight Al.e0Sis.oeOro'2.08HrO for natrolite. HzO 2,445 2.436 2,48 2.425 2,410 loss below 135'C) in tetranatrolite was con- 402 2.330 2.329 I 2.322 I 2.323 sidered to be adsorbed water; it was not used 440 2.315 2.312 I ?.28 in the calculation. With Z = 4 for the body- 2,258 centred cell, the calculated density of tetranatro- 332 2.260 2.256 2.?50 2,236 lire is 2.234 g/cm", which is slightly lower than 2.196 the measured density 2,276 glcmg. However, 422 2.196 2.195 2.'ls7 600 2.183 2.183 2.174 if H'O- is included in the calculation, the cal- 2.075 culated density becomes 2.263 g/cmg. 213 2.069 2.070 2,061 2,057 The empirical formulae for tetranatrolite and 303 1.962 the associatednatrolite are both very close to 541 'l;881 the idal formula NazAlsSisOro'2H'O.Tetrana- 323 1.877 1.825 trolite, however, is relatively enriched in K and at0 '1.8151.816 I .807 5 I .806 Ca with respect to natrolite. The enrishment of Ca and K is probably characteristic of tetrana- 70t 1.800 I .800 1.792 I trolite. A survey of the 27 analysesof natrolite 622 1.757 1.15'1 1.749 2 721 1.736 TABLE3. A,IALYSESOFTETRANATROLITE ANDNATROLITE 730 1,720 (1) (2) (3)

Si02 46.9 48.81 47.8 natrcllte and tetranatrclite may be compareddlrectly if the indlces for tetranatrc'llte are transDosedto those lor the F-cell Ti02 0.06 n.d. 0.05 by the mtrix lI0/110/00I. A1203 25.6 25.83 25.2 (2) Andersenet al. 1969. Cul(oradlation (r - t.Sqtai), quartz 0.69 0.10 'llnelntemal stanCard,Guinler-tfdgg carera. In the origlnal.data the Ca0 1.48 at 2.425Awas indexed as 501, and the line at 2.0614 Indexed as 620. Data obtaln€d by the present authors on the Mso n.d.* n.d. n.d.* mterlal frcm Greenlandare essentlally ldentical to those quoted here. Fe0 0.ll tr 0.04 NaZ0 14.0 ,14.60 16.I Kzo 1.12 tr 0.05 H20+ 9.59 10.70 9.73 natrolite is essentially identical to that of te- 1.31 tranatrolite from Greenland (Andersen et al, Heo- 1969) and is very similar to the pattern of Total .100.17 I 00.63 99.07 natrolite (Table 2). The diffraction lines 220, 310,321,411,43L,422,622and 730 are char- (l) Tetranatrolite and (3) natro'lite associated acteristic of tetranatrolite, as the corresponding with (1), ilont St-Hilaire, Qu6bec.Analyses by lines for natrolite are resolved into doublets re- electron microprobe,total Fe as FeO,H20 by TGA to l000oC. BaOand Sr0 wer€ looked for-but not sulting from the splitting of hkl and &hl pairs. detected. The splittings described may be observed on (2) Tetranatrolite, Ilfmaussaq,Greenland (Andersen carefully prepared films using 114.6 mm Debye- et aL. 1969). Scherrer cameras.A focusing camera may bring * not detected. 82 THB cANaDTANMINERALOGIST

compiled by Foster (1965) shows that only two the infrared spectra of the ordered natrolite samples (analyses 25 and 26) contain more and the presumably disordered tetranatrofite, than 2.0 wt. Vo combined CaO and K:O. similar to those differences observed for the ordered and disordered feldspars and cordierite. Sr/Ar, DrsonoER AND lNrnenso Spncrne Infrared spectra of natrolite and tetranatrolite from Mont St-Hilaire (Fig. a) were obtained It has been shcrwn that infrared sPectra are using a Beckman 4250 spectrometer and KBr sensitiveto the degreeof Si/Al order or disorder, pellets containing 2.0 mg of sample dried at as exemplified by the infrared studies on the ll0oC for 12 hours. The spectrum of natrolite feldspars (Laves & Hafner 1956, Hafner & from Mont St-Hilaire is comparable in fine Laves 1957, Thompson & Wadsworth 1957, details to the spectra of natrolite from Puyde- Martin 197O) and cordierite (Langer & Schreyer D6me (France), Poona (India) and Bohemia 1969). The main effects in the infrared spectra (Czechoslovakia) given in van der Marel characteristic of Si/Al disorder in the feldspars & Beutelspacher(1976, p.294-295). The spec- and cordierite were found to be (1) a reduction trum of tetranatrolite shows a general resem- in the multiplicity of bands due to the increase blance only to that of natrolite and is character- of symmetry and (2) a considerable increase ized by broad, more spread-out groups of bands. in half-widths (i.e., broadening) of the bands The broadening of bands is particularly pro- owing to the decreasingsimilarity of the close- nounced in the OH-stretching (320G-3600 neighbor relationship of Si and Al atoms (Laves cm'r) and the T-O-stretching (9OO-11O0 & Hafner 1962). cm-l) regions. It also shows a decrease in multi- Tetranatrolite is presumably a disordered tiplicity of bands compared with the spectrum modification of natrolite. In the structure of of natrolite. The ef,fect is more pronounced ln natrolite (Meier 196O) there are three symme- the T-O-stretching and T-O-bending (45M20 trically nonequivalent tetrahedral atoms Si(I), cm-l) regions. The infrared sp€ctrum of tetra- Si(II) and Al, the site symmetries of which natrolite is, therefore, consistent with what is are Cz, Cr and G respectively. A tetragonal expected of an Allsi disordered structural structure wilh I42d symmetry may be derived model. The minor shift of the bands toward from natrolite by disordering Si(il) and Al. lower frequencies in the tetranatrolite spectrum Si(I), however, is not required by symmetry is due, at least in part, to a slightly higher Al:Si to participate in the disorder. In the disordered ratio (Flanigen et al. l97l). struoture there are only two symmetry-non- equivalent atoms, Si(I) and (Si,Al), with site TGA eno Hvnnornsnl\4er, Stuprns symmetries Ja and Cr, rospectively. Thus, pro- nounced differences would be expectedbetween The thermogravimetric analysis of tetrana-

t o .3 E gE N

4038 36 U C23r)n % 21 n,n 9 l8 |7 t6 t5 U 13 12 ll'10 9 8 7 6 5 Wovenumbercm-trlOO Ftc. 4. Infrared spectra of tetranatrolite (A) and natrolite (B) from Mont St-Hilaire. TETRANATROLITE FROM MONT ST-HrLerne,Quinsc 83 trolite, at a heating rate of l0oC/min. in air, trolite-natrolite crystals preserved in water re- showed a slow weight-lossof l.3l% between vealed the existenceof yet another new mineral, room temperature and 135"C and a major, a higher hydrate form of natrolite. This new rapid weight-lossof 9.597o between 135 and phase, which dehydratespartially to form tetra- 435'C. Rehydration took place immediately on natrolite, is described in the following paper by cooling from 435oC to room temperature, but Chao (1980). the initial weight-loss, thought to be due to adsorbed water, was not recoverable within 12 ACKNOWLEDCEMENTS hours after cooling to room temperature. The X-ray powder pattern of the rehydrated material We thank N. M. Miles and B. C. Stone for is basically identical to that of the unheat€d preparing the infrared spectra, B. McKinstry material, except that some lines tend to be ior-preparing and monitoring the hydrothermal diffuse. Rehydration is found to be impossible expeiiments'and R. W. Yole for critically- read- if the mineral is heated to 6l5oC. The dehy- ing the manuscript. O. L. Petersen provided a drated material quenched from that temperature spicimen of tetranatrolite from Greenland and gives an X-ray powder pattern essentiallysimilar l-udith nuk"r prgvided technical assistance.This to that of metanatrolite (Peng 1955). The study was supported by NSERC grant A5113 material quenched from 820'C is amorphous. to G. Y. Chao. The TGA curve of natrolite associated with tetranatrolite shows a rapid single-stageweight- RnnBnBNcrs loss of 9.737o between 200 and 369"C, Ar.rornsew, E.K., DaNO, M. & PrrnnsrN, O.V. Tetranatrolite from Mont St-Hilaire treated (1969): A tetragonalnatrotte. Medd..Grqnland' hydrothermally at 265'C and 0.5 kbar for 7 181 (10), 1-19. days remained unchanged. Treated at 33O'C Cnao, G,Y. (1980): Paranatrolite,a new zeotte ahd 0.5 kbar for 10 days, the mineral de- from Mont St-Hilaire, Qu6bec.Can. Mineral. L8, composed to analcime with a trace of an un- 85-88. identified and M1"C and 1 kbar compound, at FleNIcBN,E.M,, Knereut, H. & Szvr"reNsrr,H.A. for 7 days tlle mineral decomposedto nepheline (1971): Infrared structural studies of and analcime with a trace of another unidentified fiameworks. Adv. Chem. ,Ser.101, 2OL-229. compound. Fosrrn, M.D. (1965): Compositionof zeolitesof the natrolite group. U.,S.GeoI. Surv. Prof. Pap. DIscussIoN 504-D. Although X-ray and infrared data suggestthat HerNen, S. & Levrs, F. (1957): Ordnung/Unord- der tetranatrolite is a disordered modification of nung und Ultrarotabsorption.II. Variation einiger Absorptionen von natrolite, its phase relationship with natrolite Lage und Intensitet Feldspiiten. Zur Struktur von Orthoklas und remains obscure. High-temperature structural Adular. Z. Krist. L0g' 204'225. studies of natrolite (Peacor 1973) showed that the Al$isOro framework stayed strongly ordered Hev, M.H. (1932): Studieson the . III. at least up to 198oC. Conunuous-heatingX-ray- Natrolite and metanatrolite,Mineral. Mag, 23' diffraction studies by van Reeuwijk (1972), 243-289. using a Guinier-Lenn6 camera, showed that na- LaNcrn, K. & Scnsvrn, W. (1969): Infraredand trolite on dehydration at 280"C transformed to powder X-ray diffraction studies on the poly- metanatrolite, which changed to another phaseat morphism of cordierite, Mgz(A1$irOt.). Amer. 510"C. However, none of these high-tempera- Mineral. 54, 1442-L459, phases ture can be related to tetranatrolite. Our Levss, F. & HAFNER,S. (1956): Ordnung/Unord- attempt by hydrothermal experiments to reorder nung und Ultrarotabsorption.I. (Al, Si)-Vertei- Al and Si in tetranatrolite also was unsuccess- lung in Feldspiiten.Z. Krist. 108, 52-63. ful. Thus, it seemsthat factors other than tem- (1962): absorPtionef- perature and pressure, such as stoichiometry, & - Infrared fects, nuclear magnetic resonanceand structure may have played important roles in the forma- of feldspars.Norsk Geol. Tidsskr. 42(2), 57-71. tion of tetranatrolite. The introduction of Ca in- to the structure of natrolite may promote the Men'nN, R.F. (1970): Cell parametersand in- disorder of Al and Si during crystallization and, frared absorption of synthetic high to low albites. subsequently, may serye to stabilize the disor- Contr, Mineral. Petrology 26, 62-74. dered structure. Mrrrn, w.M' ( 1960): The of Further studies of fresh, composite tetrana- natrolite. Z. Krist. LL9, 430'444. 84 THE CANADIAN MINERALOGIST

Persr, A. (I971')t Natrolite from the Green River vAN DER Menrr, H.W. & Brurrlsrecnet, H. Formation, Colorado, showing an intergrowth (1976): Atlas of Infrared Spectroscopy of Clay akin to twinning. Amer. MineraL S6, 560-569. Minerals and their Ad,mirtwes. Elsevier, Amster- dam. Peecon, D.R. (1973): High-temperature, single- crystal X-ray study of natrolite. Amer. Mineral. vAN REEuwr.rx, L.P. (1972): High-temperature 58, 676-680. phases of zeolites of the natrolite grotp. Amer. Mineral, 57, 499-510. PnNc, C.J. (1955): Thermal analysis study of the natrolite group. Amer. Mineral. 40, 834-856. Tnor'rpsoN, C.S. & Weoswontr, M.E, (1957): Determination of the composition of plagioclase feldspars by means of infrared spectroscopy. Received August 1979, revised rnanuscript accepted Amer. Mineral. 42, 334-341. October 1979.