Zunyite Was Originally Described from the Zuni Mine, Colorado

MINING GEOLOGY, 36(3), 219•`230, 1986

The Stability Relationships of Zunyite Under Hydrothermal Conditions

L. C. HSU*

Abstract: The stability relationships of zunyite, Al13Si5O20F2(OH, F)16Cl , were determined at Pi=1kb and T=300-600•Ž in solutions with constant HCl=1M but different HF=0.1 to 20M. The products of stoichiometric

oxide mix seeded with natural zunyite in respective solutions at 400•Ž were used as starting materials. The stability

field of zunyite is rather limited; it is stable in a solution with HF concentrations no more than 2M. In 1M HF solu-

tion, zunyite is stable up to 450(5)•Ž and is replaced by topaz at higher temperatures. It appears to remain stable at

the same temperature range in solutions with HF as low as 0.1M. In solution with HF concentration of 3M, topaz is

stable at temperature above 470(5)•Ž. At lower temperatures topaz is accompanied by AlF3 phase. This assemblage

is also stable at higher temperatures in solutions with HF concentrations up to 10M. In solutions with high HF con-

centrations, quartz+AlF3 become stable. The rare occurrence of zunyite compared to topaz is the consequnce of

stringent chemical conditions aside from temperature. Both F and Cl are indispensable for the mineral and yet

higher F activities destabilize it. The occurrence of zunyite as a massive body in altered felsic volcanics reported

elsewhere is thus indicative of unusual solution behavior and physico-chemical condition during the alteration.

Introduction timate intergrowth of zunyite and quartz,having as much as 75 percent zunyite by volume Zunyite was originally described from the with local solid pure zunyite. The texture sug- Zuni mine, Colorado (HILLEBRAND,1885). It gests that the lode is a replacement product of was subsequently found in adjacent mining andesitic country rock. districts in Colorado (PENFIELD,1893; BUR- The significance of zunyite may well be a BANK, 1932) and in Utah (LOVERINGand double one. In its own right zunyite is signifi- STRINGHAM,1945). In these places the mineral cant as a mineral resources, e.g. used for is commonly found in altered and silicified refractory material (MASUIand SHIMIZU,1944), igneous rocks as alteration product of feld- used as catalytic cracking to improve gasoline spars and/or as gangue mineral in yield (ENGEBRETSON,1965), used as aluminum metalliferous vein. Similar occurrence of source along with alunite in future (HALL, zunyite was reported in other parts of the 1978), and possible source of fluoride. Zunyite world, e.g. Algiers (TURCO, 1962a), Burma is a mineral characteristic of advanced argillic (BARIC and ZALOKAR, 1965), Morocco alteration (MEYER and HEMLEY, 1967) and (LABLANC,1970), Puerto Rico (HILDEBRAND, occurs almost exclusively in altered and 1961) and Ukraine (KLITCHENKOet al., 1976). mineralized zones in association with fluorite, Recently a huge zunyite lode with an outcrop topaz, Be-minerals, and many sulfide ore of about 1200 ft. long and 10 to 60 ft. wide, minerals (e.g. DIETRICH,1965; HILDEBRAND, forming a cliff as much as 10 ft. high was 1961; KASHIKAIand ALIEX, 1960). Thus the oc- discovered in Elko County, Nevada (COATS,et currence of zunyite in certain assemblage may al., 1979). The zunyite lode is a fine-grained in- serve as a clue to discovery of certain economic mineral deposits. Received on February 3, 1986, Accepted on March 23, Zunyite is one of the few minerals to con- 1986. * Nevada Bureau of Mines/Geology and Department of tain as many as three different volatile com- Geological Sciences, Mackay School of Mines, Universi- ponents, viz, H2O, F and Cl. All these three ty of Nevada, Reno, Nevada 89557, USA. components are the essential constituents in Keywords: Zunyite, Topaz, A1F3, Hydrothermal altera- hydrothermal solutions capable of carrying tion, Hydrothermal synthesis, Stability relation. and depositing minerals of economic value

219 220 L. C. HSU MINING GEOLOGY

Table 1 Materials used in experiments and significance. Experimental investigation with an aim to synthesize zunyite and to deter- mine its thermal stability were almost exclusively conducted by the European scholars, particularly in France. There were conflicting results obtained in different laboratories. ALTHAUS (1966) claimed a success in synthesiz- ing F-free zunyite from a hydrothermal system containing quartz, kaolinite, pyrophyllite and HCl solution. BAUMER and TURCO (1968) after reproducing the experimental conditions of ALTHAUS, however, concluded that the synthetic product was in fact Al24O11(OH)44Cl6 rather than zunyite. On the other hand, TURCO

(1962a, b) stressed that the presence of F was essential for the formation of zunyite but Cl was not so. The region of stability lies between * Prepared from: 470-600•Ž under unspecified Pf (fluid pres- Fisher Scientific conc. HCl solution, 37.5%, sp. gr. 1.18. Mallinckrodt Chemical conc. HF solution, 48%, Sp, gr. 1.2. sures). In all these experiments, either concen- trated acids or solid compounds (AlF3 and after 2 to 5 months run depending on AlCl3¥6H2O) were used for source of F and Cl temperature. In this way the fugacities of the and the duration of runs was only several days volatile components may be controlled by the at most. Thus, it is no surprise to have conflict- initial solution compositions and the reactions ing results, because either the experimental may approach as closely as possible to conditions deviated too far from the natural equilibrium. For synthesis of F-free zunyite, ones and/or the equilibrium of reactions was pure HCl solutions of different concentrations seldom attained. In this investigation, it is with products of seeded oxide mix were used hoped that the stability relations and chemical in repeated runs. Seeded solid mix containing composition of zunyite can be determined une- AlCl3, Al2O3 and SiO2 was also used but not quivocally by adopting different experimental for repeated run. Synthesis of Cl-free zunyite approaches. Such information will, in turn, was conducted in a similar way, except that serve as a key to the understanding of natural seeded solid mixes used allowed different F/ hydrothermal environment under which eco- OH proportions. nomic minerals along with zunyite are depos- The possible crystalline phases in the system ited. Al2O3-SiO2-H2O with HF and HCl as addi-

Experimental tional components are shown in Fig. 1 where abbreviation of each phase is also indicated. The stability relationships of zunyite were determined at Pf=1 kb and T=300 to 600•Ž Results in solutions with constant HCl=1M but Description of Synthetic Phases different HF=0.1 to 20M (Table 1). The pro- Zunyite: The structure of zunyite (Fig. 2) is ducts of stoichiometric oxide mix of ƒ¿- built up of unique Si5O16groups of linked Si- cristobalite and Al2O3¥XH2O seeded with tetrahedra combined with Al12O16(OH)30 natural zunyite in respective solutions at groups of linked Al-octahedra. The arrange- 400•Ž were used as starting materials. Each ment requires the inclusion of at least two F run contains 50 mg charge and 50 ƒÊl solution atoms per stoichiometric molecule resulting in of respective composition sealed in a Ag30Pd70 the formula for the mineral. The 13th Al atom capsule 20 mm•~3 mm size. The respective is in tetrahedral coordination, the AlO4 solution was replenished 2 to 3 times each tetrahedra being isolated from SiO4 tetrahedra 36(3), 1986 Stability of zunyite under hydrothermal conditions 221

Fig. 1 Crystalline phases in the system Al2O3-SiO2- H2O-HF-HCl. Open circles and rectangles are phases containing volatile components.

Fig. 3 Synthetic zunyite: (a) photomicrograph as grain mounting in n=1.480 immerion oil, plane light; (b) scanning electron photomicrograph. Run products ZNE5a and ZNE3b, respectively.

it defies detailed study under petrographic microscope (Fig. 3a). Its characteristic tetrahedral form is, however, well-revealed under scanning electron microscope using secondary electron detector (Fig. 3b). With calibrated Co powders as internal standard (2ƒÆ CuKƒ¿ for

Co 104=35.183•‹), the synthetic zunyite has a =13.870-13.899(3)•ð based on 333/511 reflec-

Fig. 2 Crystal structure of zunyite after PAULING tion. Thus the synthtic zunyite show minor (1933), KAMB (1960), and LOUISN.ATHANand GIBBS compositional variation but to a less extent (1972); (a) group of five silicon tetrahedra, [Si5O16] than that by TURCO (1962a, b) which has a= , (b) group of twelve aluminum octahedra [Al12O16 13.85 to 13.92 •ð. BAUMER (1975) shows that (OH)30], (c) a portion of the zunyite structure: one his synthetic hydrozunyite (OH- replacing

AlO4 tetrahedron is marked with Al; smaller SiO4- 4) has a=13.904(5)•ð. Natural zunyite spheres represent O2-, larger Cl- ions. from the Zuni Mine has a=13.820 (PAULING, 1933) and that from Nevada has a=13.850 •ð. and other AlO6 octahedra and the Cl atom oc- It appears that the synthetic zunyite may be in- cupying cavities in the framework. variably more hydrous than the natural one.

The synthetic zunyite is so fine-grained that The Cl-free zunyite was metastably synthe- 222 L. C. HSU MINING GEOLOGY

Fig. 4 X-ray powder diffractograms of zunyites: (a) natural zunyite from Nevada, (b) synthetic zunyite ZNE3b; (c) synthetic Cl-free zunvite ZNM7.

sized from seeded solid mix M; such zunyite thoroughly mixed KBr and 0.2% zunyite has a=13.858-13.872(3)•ð. The X-ray powder powders were peletized into a clear disk under diffractograms of natural zunyite, synthetic 65 tons per square inch pressure. The IR ab- zunyite and synthetic Cl-free zunyite are sorption spectra of these zunyites are shown in shown in Fig. 4. Fig. 5. The synthetic zunyite shows a strong ab- The infrared absorption spectra of these sorption band at 3330 cm-1, a weaker one at zunyites were obtained on a Perkin-Elmer 3630 cm-1, and a still weaker but sharp one at Model 599 double-beam spectrometer in the 3678 cm-1. These bands are probably due to 200-4000 cm-1 range. About 350 mg of the presence of hydroxyl groups. The last 36(3), 1986 Stability of zunyite under hydrothermal conditions 223

Fig. 5 Infrared absorption spectra of zunyite: (a) natural zunyite from Nevada; (b) synthetic zunyite ZNE3b; (c) synthetic Cl-free zunyite ZNM7. 224 L. C. HSU MINING GEOLOGY

band is, however, not observed in the natural zunyite. It is not clear why the strongest absorption band at 3330 cm-1 is missing in the synthetic Cl-free zunyite, although the other two are present but much weaker. There are also minor differences found in the low-fre- quence absorption bands for the Cl-free zunyite as compared with the normal ones. Topaz: Topaz synthesized in the system with zunyite bulk composition exists either alone or with AlF3. ROSENBERG(1972) recognized two main types of compositional variation in synthetic topaz: a "natural" series having Fig. 6 Photomicrograph of Topaz and AlF3 replac- variable F/OH ratios and an OH-free solid ing zunyite as grain mounting in n=1.550 immersion oil, plane light, ZND12b. Af: AlF3, Tp: solution series containing excess Al and F. Topaz, Zn: zunyite. Since the bulk composition of zunyite contains higher Al/Si ratio than topaz, the topaz synthesized alone at higher temperatures replacing zunyite may belong to the second series with excess Al and F, while the topaz coexisting with AlF3 may belong to the "natural" series with variable F/OH ratios . The F content of the topaz coexisting with AlF3 in 5M HF/1M HCl solution at different temperatures was found to be 15.3 to 16.2 wt% using the X-ray method of RIBBEand ROSENBERG(1971); the higher temperature topaz contained higher F content. The topaz

collected from cavities in the topaz rhyolite Fig. 7 Photomicrograph of AlF3 and quartz as from southern Wah Wah Mountain, Utah grain mounting in n=1.480 immersion oil, plane contains 20.1 wt%F. Such topaz is regarded as light, ZNA7. Af: AlF3. a product of vapor-phase crystallization from a vapor extremely rich in F released from lavas ture did not take place at lower temperatures during cooling and devitrification (e.g. CHRIS- as was observed by ROSENBERG(1972). AlF3 TIANSENet al., 1984, CHRISTIANSENet al., 1983). coexisting with quartz is shown in Fig. 7. Topaz and AlF3 replacing zunyite is shown in Other phases: Hydrous aluminosilicates such Fig. 6. as pyrophyllite, boehmite, gibbsite, and AlF3: This phase occurs in solutions of high diaspore grew metastably at the early stage of HF concentration; in relatively lower HF con- experiments. They essentially gave way to centrations it is associated with topaz but in more stable phase or phase assemblage. X- higher HF concentrations it coexists with aluminosilicate (Xa) phase appears erratically quartz. AlF3 crystals occurring in any solution in terms of temperature and solution composi- and at any temperature are rhombic in form tion. The X-ray powder diffraction pattern of with nearly square appearance and having this phase matches very closely to that of space group of R32. Measurements of the four AS(H)II of ARAMAKI and Roy (1963). Ac- most intense X-ray powder reflections, 110, cording to them, AS(H)II is not strictly an Al2 210, 220 and 321 indicate that AlF3 remain SiO5 composition but has a variable com- essentially anhydrous. This may explain why position possibly with ratios of Al2O3/SiO2 inversion to ralstonite with pyrochlore struc- higher than unity and OH- ions replacing 36(3), 1986 Stability of zunyite under hydrothermal conditions 225

Fig. 8 Stability field of zunyite, run data for Solution A are not shown.

some of the O2- ions. The metastable appear- tion up to 10M. In solutions with HF concen- ance of Xa phase was also reported by many in- tration higher than 10M, the assemblage, vestigators (e.g. ALTHAUS, 1965; CARR and quartz+AlF3, becomes stable. The results of FYFE, 1960; TURCO, 1964). the experiment are listed in Table 2. Attempts Stability of Zunyite to synthesize F-free zunyite from oxide mix in Zunyite was first synthesized hydrothermal- Solutions I, J, and K and from solid mix L all ly by TURCO (1962a, b). As shown in Fig. 8, seeded with natural zunyite at 400-500•Ž the stability field of zunyite is rather limited; it failed. Xa and various hydrous aluminosili- is stable in a solution with HF concentration cates and occasional chlor-aluminate ap- no more than 2M. In 1M HF solution, zunyite peared instead. This result confirms the fun- is stable up to 450(5)•Ž but it is replaced by damental role of F in the zunyite structure. Cl- topaz at higher temperatures. It appears to re- free zunyite was synthesized from seeded solid main stable in the same temperature range in mix M at temperatures between 300•Kand solutions with HF concentration as low as 500•Ž. Cl-free zunyite did not form in other 0.1M. In solution with HF concentration of seeded solid mixes, indicating high F content 3M, topaz alone is stable at temperatures is not favored. Seeded oxide mix in Solutions above 470(5)•Ž; at temperatures below that, F, G and H invariably yield topaz and other topaz is accompanied by AlF3 phase. This phases in addition to Cl-free zunyite. On fur- topaz+AlF3 assemblage is stable at all ther run, all Cl-free zunyites were eventually temperatures in solutions with HF concentra- demonstrated to be metastable and were 226 L. C. HSU MINING GEOLOGY

Table 2 Run data for zunyite. In each run product, the relative abundance of phases are listed in decreasing order downward. Phases interpreted as stable are in heavy letters. There are as many times of solution replenishment as there are as many columns in each charge number. The number at the bottom of run product indicates the duration of run in days. Combination of solution or solid mix symbol and run number after ZN yields the designation for run product, e.g. ZNE3b. 36(3),1986 Stability of zunyite under hydrothermal conditions 227

Fig. 9 Location of Nevada zunyite lode in Elko (E) County. 228 L. C. HSU MINING, GEOLOGY replaced by topaz with or without AlF3. Thus, all the three volatile components, H2O, F, and Cl are indispensable for the stability of zunyite.

Discussion

Zunyite is a relatively rare mineral characteristic of advanced argillic alteration and occurs almost exclusively in altered and mineralized zones of many sulfide ore deposits. Other types of occurrence for zunyite are less common but are described elsewhere, e.g. in Precambrian aluminous shale (VERMAAS, Fig. 10 Outcrop of massive zunyite lode at the west 1952) and in secondary quartzites and schists end in Nevada. Facing north. Coarse debris fallen from the outcrop are scattered in the foreground. (LOGINOV, 1944). The massive zunyite lode in Nevada (COATS, et al., 1979) is located in the western margin of Elko County, forming a small ridge at an elevation between 6,440 and 6,480 ft. (Fig. 9). Outcrops and distribution of coarse debris sug- gest its total length is about 1,200 ft., generally trending N80•KW. At the west end it forms the widest and cliffy outcrop which rises as much as 10 ft. high above the steeper slope to the south (Fig. 10). The width of the lode appears to range from 10 to 60 ft., but the actual contact is obscured by talus from the higher Fig. 11 Photomicrograph of massive zunyite inter- portions. The zunyite lode appears dazzlingly white from distance, when not coated with growing with quartz. Rutile and iron ore are relict mineral, plane light. Mt: magnetite, Qz: quartz, brown limonitic matter. The pure zunyite lode Rt: rutile, Zn: zunite. is very fine-grained and has the appearance of unglazed porcelain. Relict minerals are ob- stable complexes. Therefore, in almost all served in intergrown mass of zunyite and hydrothermal fluids the Cl/F ratios are in- quartz (Fig. 11). Traces of original porphyritic variably much higher than unity (e.g. ELLIS, texture suggests that the lode developed along 1979). In the presence of chlorine in most a near E-W trending fracture zone through hydrothermal solution, it is the availability of hydrothermal alteration by replacing andesitic fluorine which is critical to the formation of and dacitic country rocks, of possible Tertiary zunyite. On the other hand, the presence of age. chlorine in solutions, say containing 1M HCl, Fluorine is not generally an abundant does not inhibit the formation of topaz nor its constituent of the magmatic aqueous phase, stability and thus the occurrence of topaz say, in most porphyry copper systems alone without association of zunyite does not (BURNHAM, 1979), nor in geothermal water indicate the lack of chlorine in the solution. (ELLIS, 1979). In contrast, chlorine forms The rare occurence of zunyite compared to neither stable chloride minerals nor complexes topaz is not only due to the requirement of the with silicon or aluminum at magmatic presence of the third volatile component, temperatures in silicic systems. In aqueous chlorine, but also due to the stringent condi- solution of magmatic temperatures NaCl, tion imposed on the fluorine activity in addi- KCl, HCl. CaCl2 and (FeCl2+FeCl3) are tion to temperature for the stability of 36(3), 1986 Stability of zunyite under hydrothermal conditions 229

zunyite. Both F and Cl are indispensable to R. Acad. Sci., Paris, Ser. D, 267, 467•`470. the stability of zunyite and yet higher F ac- BURNHAM, C. W. (1979): Magmas and hydrothermal fluids. In Geochemistry of Hydrothermal Ore tivities destabilize the mineral. The present Deposits (H. L. BARNES, ed.), 71•`136. study establishes the upper concentraction CARR, R. M. and FYFE, W. S. (1960): Synthesis fields of limit of 2M HF solution for the stability of some aluminosilicates. Geochim. et Cosmochim. zunyite. Even the solution concentration is Acta, 21, 99•`109.

satisfactory, the mineral cannot remain stable CHRISTIANSEN, E. H., BIKUN, J. V., SHERIDAN, M. F. and

at temperatures above 450•Ž. The association BURT, D. M. (1984): Geochemical evolution of topaz

of zunyite and topaz in some hydrothermal rhyolites from the Thomas Range and Spor Moun- deposits below their equilibrium temperature tain, Utah. Am. Mineral., 69,223•`236. of 450•Ž may reflect the fluctuation of HF CHRISTIANSEN, E. H., BURT, D. M., SHERIDAN, M. F. and concentration and/or intermittent supply of WILSON, R. T. (1983): The petrogenesis of topaz Cl in hydrothermal solutions. The massive rhyolites from the Western United States. Contrib. Mineral. Petrol., 83, 16•`30. zunyite lode in Nevada, in which topaz does COATS, R. R., CONSUL, J. J. and NEIL, S. T. (1979): not occur but quartz instead, appears to re- Massive zunyite rock from Western Elko County, quire some unusual physico-chemical.condi- Nevada. U. S. Geol. Surv. Open-File Report 79•`764, tions, i.e. a steady and prolonged supply of 10p.

low temperature (•ƒ450•Ž) hydrothermal solu- DIETRICH, J. E. (1965): Zunyite D'Azrou-Melloul.

tion with low HF concentration (•ƒ2M) in the Morocco Service Geologic Notes et Mem., No. 183,

presence of Cl. The failure of AlF3 to occur in 105•`107.

nature is probably due to the fact that ELLIS, A. J. (1979): Explored geothermal systems. In

hydrothermal solution never contains HF Geochemistry of Hydrothermal Ore Deposits (H. L. above 3M concentration and/or that the rock BARNES, ed.), 632•`683. ENGEBRETSON,G. R. (1965): Conversion of hydrocarbons bulk composition seldom reaches Al/Si ratio to gasoline with a zunyite-containing catalyst com- of 13/5 and above. posite. Rept. to Sinclair Research Inc. Acknowledgement: Critical review of the HALL, R. B. (1978): World nonbouxite aluminum manuscript by T. SHOJI of the University of resources•\Alunite. U. S. Geol. Surv. Prof. Paper

Tokyo is gratefully acknowledged. This study 1076, 35p.

was supported by the Research Advisory HILDEBRAND, F. A. (1961): Hydrothermally altered rocks

Board, University of Nevada, Reno. in eastern Puerto Rico. U. S. Geol. Surv. Prof. Paper

References 424-B, 219•`221. HILLEBRAND, W. F. (1885): On zunyite and guitermanite ALTHAUS, E. (1966): Der Stabilitatsbereich des two new minerals from Colorado. Colorado Sci. Pyrophyllits unter dem Einfluss von Sauren: I. Mi Soc. Proceedings, 1, 124•`132.

t-eilung Experimentelle Untersuchungen, Contrib. KAMB, W. B. (1960): The crystal structure of zunyite. Acta

Mineral. Petrol., 13, 31•`50. Crystallogr., 13, 15•`24. ARAMAKI, S. and Roy, R. (1963): A new polymorph of KASHIKAI, M. A. and ALIEV, V. I. (1960): Zunyite and Al2-SiO5 and further studies in the system Al2O3- zunyite-bearing rocks. Trudy Akademia Nauk Azer- SiO2-H2O. Am Mineral., 48, 1322•`1347. baidzhanskoi SSR, Baku Institute Geologil. Tom 20, BARIC, L. and ZALOKAR, B. (1965): Note on the occurrence 5•`35.

of zunyite at Monywa, Burma. Bull. Sci. Conseil KLITCHENKO, M. A., KRAMM, T. P. and KOBKOV, A. V. Acad, RPF Yougoslavie, 10, 48•`49. (1976): Findings of zunyite in the Ukraine. Dopov BURBANK,W. S. (1932): Geology and ore deposits of the Akad, Nauk Ukr. RSR, Ser. B, 2, 105•`108.

Bonanza Mining district, Colorado. U. S. Geol. LABLANC, M. (1970): Roches a pyrophyllite, zunyite et

Surv. Prof. Paper 160, 166p. diaspore clans la precambrin II du Graara oriental BAUMER, A. (1975): Donnees de diagramme de ponder (Anti-Atlas central). Morocco Service Geologic d'une hydrozunyite de synthese de formule Al13Si3 .7- Notes et Mem., No. 275, 153•`154. O14.8(OH)14.5F9.7. Bull. Soc. Fr. Mineral. Crystalogr. LOGINOV, V. P. (1944): Hypogenetic relict minerals in the

98, 257•`258. wall rocks of the Kabanskoye pyrite deposit (the

BAUMER,A. and TURCO,G. (1968): Essais de synthese de la middle Urals). Bull. Akad. Sci. SSSR, Ser. Geol.,

zunyte exempte de fluor par voie hydrothermale. C. No. 5, 106•`112. 230

LOVERING, T. S. and STRINGHAM, B. (1945): Zunyite in ROSENBERG, P. E. (1972): Compositional variations in

Utah. Am. Mineral., 30, 76•`77. synthetic topaz. Am. Mineral., 57, 169•`187.

MASUI, J. and SHIMIZU, Y. (1944): "Kochite", a zunyite- TURCO, G. (1962a): La zunyite: Recherches experimen-

diaspore-sericite rhyolites from Ishidoriya, Iwate tales physicochimiques en liason avec l'etude du

Prefecture. Jour, Japanese Assoc. Mineral. Petrol. nouves gisement de Beni-Embarck. Bull. Soc. Franc.

and Econ. Geol., 32, 105•`111. Mineral. Crystallogr., 85, 407•`457.

MEYER, C. and HEMLEY, J. J. (1967): Wall rock alteration. TURCO, G. (1962b): Synthese hydrothermale de la zunyite.

In Geochemistry of Hydrothermal Ore Deposits (H. Comptes Rendus de l'Acadenie des Sciences, Paris,

L. BARNES, ed.), 166•`235. 254, 2382•`2385.

PALLING, L. (1933): The crystal structure of zunyite TURCO, G. (1964): Formation d'un nouveau silicate

Al13Si5O20(OH, F)18Cl, Z. Kristallogr., 84, 442•`452. d'aluminium de formule Al2SiO5 au cours de la syn-

PENFIELD, S. L. (1893): Mineralogical notes. Am. J. Sci., these hydrothermale de la zunyite. Comptes Rendus

3rd Ser., 45, 396•`399. de l'Academie des Sciences, Paris, 258, 3331•`3334.

RIBBE, P. H. and ROSENBERG, P. E. (1971): Optical and X- VERMAAS, H. S. (1952): Zunyite from Postmasburg, South

ray determinative methods for fluorine in topaz. Am. Africa. Am. Mineral., 37, 960•`965. Mineral., 56, 1812•`1821.

ズニ石の安定関係

許良基

要旨:HCl(1M)とHF(0.1～20M)を含む溶液を用い 470℃ 以上ではトパーズが安定で,それ以下の温度ではて,ズニ石, Al13Si5O20F2(OH, F)16Clの安定関係を1kb, トパーズにAlF3相が加わる.この組合せの安定領域は, 300～600℃ で決定した.上記の組成となるように酸化 HF濃度の上昇とともに高温側に広がる.HFが10M

物を混合し,これに天然産のズニ石を種として加え, のような高濃度の領域では,石英+AIF3が安定となる.

400℃ の溶液で処理した産物を出発物質とした .ズニ石ズニ石の産出がトパーズに較べて稀なのは,温度の他の安定領域は比較的狭く, HF濃度が2M以下の溶液中に,化学的条件が限られていることによる.FとClはでのみ安定である.1MのHF溶液中で,ズニ石は450℃ この鉱物にとって不可欠である,しかし,Fの活動度がまで安定であり,これ以上の温度ではトパーズに変わ上昇すると不安定になる.珪長質火山岩の変質帯にズニる.HF濃度がこれ以下の場合,ズニ石の安定な温度の石が塊状をなして産出するのは,変質時における極端な上限はほとんど変化しない.HF濃度が3Mの場合, 溶液の挙動と物理化学的条件を物語っている.