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The formation of analcime from laumontite in the Smrekovec volcanics, Northwest Slovenia - an experimental approach
J. Weitkamp, H.G. Karge, H. Pfeifer and W. HBlderich (Eds.) Zeolites and Related Microporous Materials: State of the Art 1994 Studies in Surface Science and Catalysis, Vol. 84 0 1994 Elsevier Science B.V. All rights reservcd.
299
The formation of analcime from laumontite in the Smrekovec volcanics, Northwest Slovenia - an experimental approach U. Barth-Wirsching", D. Klammef' and P. Kovic-Kraljb 'Institute of Engineering Geology and Applied Mineralogy, University of Technology Graz, Austria bGeological Survey of Ljubljana, Slovenia Summary: Analcime was formed at the expense of laumontite ,duringthe last stage of the alteration processes of the andesitic to dacitic volcanic rocks of the Smrekovec complex in Northwest Slovenia. Experimental investigations showed that this alteration is possible in either a closed system with concentrated sodium solutions, such as sea water, at low temperatures (I 100°C) or in an open system with dilute sodium solutions, such as hydrothermal solutions or heated surface waters, at elevated temperatures (r 200'C).
1. INTRODUCTION
The Upper Oligocene Smrekovec volcanic complex in Northwest Slovenia comprises an approximately 60 meters thick sequence of andesitic to dacitic rocks. These have undergone alteration processes by circulating solutions heated by rising small intrusive bodies emplaced at shallow depths [l]. Because the base of the Smrekovec volcano is assumed to be on the seafloor while the summit region probably was subaerial the reaction of different solutions was facilitated (a) concentrated solutions, i.e. seawater, (b) dilute solutions, i.e. hydrothermal or heated meteoric waters. The alteration history is rather complex and involves at least three different stages. The alteration reactions are characterized by the formation of zeolites (laumontite, mordenite, clinoptilolite, heulandite, thomsonite, stilbite, yugawaralite and analcime) and other silicate minerals, including quartz, albite, chlorite, interstratified chlorite/smectite and sphene. Among the observed zeolites, laumontite is the most common and widespread one. During the last stage of alteration laumontite - and to some extent albitized plagioclase - became instable and were altered to analcime. The formation of analcime was accompanied by changes of the interstratified chlorite/smectite minerals: the original content of the smectite component amounting to 20% and lo%, respectively, increases to 60%. Typical analcime containing alteration
300
products comprise analcime (up to 40 wt.%), interstratified chlorite/smectite, albite,
+ quartz, and 5 potash feldspar. In the most extensively altered parts quartz has been
partly or completely leached. In areas nearer to the intrusive body the alteration of laumontite to albite is observed. Besides the above-mentioned kind of analcime formation, analcime occurs in veins characterized by cube-like morphology. Till now a lot of experimental work was done on alteration reactions of various materials, like feldspars [2], nepheline [2,3,4], sodalite [4], heulandite and clinoptilolite [5], clinoptilolite tuff [6] and volcanic glasses [ 11, resulting in the formation of analcime. However, no experiments on the formation of analcime at the expense of laumontite were reported. Therefore, the aim of our experiments was to alter a rock material from the Smrekovec volcanic complex containing laumontite and albitized plagioclase into analcime containing alteration products, under conditions approaching the natural ones as close as possible, in order to investigate under what conditions the alteration may have taken place yielding products as similar as those formed in nature. 2. EXPERIMENTAL
The starting material used in the experiments had the following mineral contents: laumonite (-20 wt.%), albite (15-20 wt.%), interstratified chloritehmectite (50-55 wt.%), quartz (< 5 wt.%), potash feldspar in traces. 0.5g material of grain size < 0.09 mm (90% < 3 0 p ) were reacted with 25 ml solution of the following composition: distilled water, 0.01N NaC1,O.OlN NaOH, 0.01N CaCl,, O.lN CaC1, and solution mixtures (1:l) of 0.01N NaOH + 0.01N NaCl, 0.01N NaOH + 0.1N NaC1, 0.1N NaOH + 0.1N NaC1, 0.01N NaOH + 0.01N CaC1, and 0.01N NaOH + 0.1N CaCl,. Experiments were carried out without stirring in both closed (reaction times 20, 80,200 days) and open systems (change of solution every 20 days) in the temperature range between 50' and 250°C at autogenous pressure. All syntheses were performed twice in Teflon-coated stainless steel pressure-vessels of 70-ml capacity. The alteration reaction in a closed system is equivalent to the reaction in a closed pressure-vessel. A hydrologically open system characterized by slow percolation of solutions, that allows the addition and removal of cations to and from the reacting system, was simulated by stopping the reaction after certain periods then separating the solution from the solid followed by renewing of the solution. Reaction products were investigated by X-ray powder diffraction (XRD; Philips PW 1840, Cu-Ka radiation) and scanning electron microscopy (SEM; Cambridge Mark 2A instmment).
301
3. EXPERIMENTAL RESULTS The alteration products of the experimental runs with distilled water as well as with Ca- and Na-Ca-solutions showed that the formation of measurable amounts of analcime at the expense of laumontite and albitized plagioclase, respectively, requires a reaction with Na-dominated solutions according to the equation Ca[Al,S!40,2] * 4H2O + 2Na' + 2 Na[AlSi,O,] * H,O + Ca2' + 2H,O laumontite analcime The experimental runs with Na-solutions show that formation of analcime is possible at these conditions in both closed and open systems. In both systems analcime forms in the temperature range between 2 75' and 5 250°C. However, it is only stable up to temperatures of 5 200'C depending on the concentration of the reacting solution. At all conditions, analcime formation starts on the surface of laumontite or albite. Tables 1 and 2 show the experimental results formed at those experimental conditions yielding high amounts of analcime.
3.1. Closed system The amounts of analcime formed by alteration in closed system depend on the reacting solution. Dilute Na-solutions have to be alkaline to form noticeable amounts of analcime. The maximum amount is about 10 wt.% at the reaction of 0.01N NaOH at 200'C after 200 days. On the other hand, with a concentrated Na-solution the maximum amounts increase up to 45-55 wt.% at temperartures of 150"and 200'C after 200 days (Table 1). Accordingly, the laumontite content decreases to about 80% of the initial content in experimental runs with low-concentration solutions, whereas laumontite as well as potash feldspar and quartz disappear completely in solutions of high concentrations. Albite content decreases at all temperatures except at 250°C corresponding to the instability of analcime at this temperature. This is shown by limitations in analcime morphology formed in dilute solutions and the decreasing amount of analcime observed in the reaction products formed with concentrated solutions during increasing reaction periods (Table 1). However, the instabability of analcime in such solutions starts already at 200'C as can be seen by SEM showing residues of former analcime crystals. In addition to analcime, traces of mordenite form with highly concentrated solutions at elevated temperatures (3 150°C). Small amounts of poorly crystallized smectite are formed in the alteration products of most experimental runs at temperatures below 200°C. The morphology can be defined by the size ratio of the (100)- and (21 1)-faces which decreases with increasing temperature, reaction time, pH, and concentration of the reacting solution, respectively. Analcime with cubic morphology is formed at temperatures of 5 lOO"C, only. The size of the analcime crystals, too, is influenced by the factors mentioned above. The largest crystals 20 pm) form during the reaction in the highly concentrated solution. Additionally, several generations of analcime crystals form in this solution and differ in the size ratio of (100) to (21l), the crystal
Table 1 Analcime formation from the material used during the experimental alteration in closed system with 0.1N NaOH + 0.1N NaCl Temperature Time Lau (exp) ('C)
50 75 100 150
200
250
(days) Lau(start)
200 200 80 200 20
80 60 -70 70 10 -30 0
Yox 100
Kf, Q, Ab Kf, Q, Ab Kf,Q, Ab (Kf, Q) Ab Kf,Q,Ab
Analcime formation
SEM
XRD
(A) A (30 - 15 wt.%) A ( -40 wt.%)
80 200 20 80
A A A A
200
A (45 - 50 wt.%)
( -40 wt.%) (45 - 50 wt.%) ( -40 wt.Yo) (40 - 45 wt.%)
A (
-4Owt.%)
80
A (
-55 wt.%)
200
A (
-45
20
0
Ab
wt.%)
A (100) A (100)>> (211) A (100)>> (211) A (loo)>> (211) (211)>> (100) A (211)>> (100) A (211)>> (100) A (loo)>> (211) A (loo)>> (211) (211)>> (100) A (211) >>>(100) (211)>> (100)
-1pm
-2w -3pm
2- 3w 2- 3p
c 5 pm 1.5 pm
2- 3 5 pm 5 pm -20 pm 5 - 10 pm dissolution of analcime A (100)>> (211) 2 - 3 pm (211)> (100) -5pm A 5 pm (211)>> (100) 120 pn A dissolution of analcime
Lau (exp) : Laumontite content in the experimentally formed alteration products Lau (start) : Laumontite content in the starting material - = no analcime formation; ( ) = small amounts of a mineral; A = analcime; Kf = potash feldspar; Q = quartz; Ab = albite
-
-
+ mordenite + mordenite +mordenite
+ mordenite + mordenite
+ mordenite
W
E
Table 2 Analcime formation from the material used during the experimental alteration in open system with 0.01N NaOH Temperature Time Lau (exp) ('C)
150
200
250
(days) Lau(start) 80
100 120 140 160 180 200 20 40 60 80 100 120 140 160 180 200 20 40
60
80 75 80
% x 100
(Kf, Q) Ab (Kf,Q)Ab (Kf,Q)Ab 80 (Kf, Q)Ab 65 -70 (Kf, Q) Ab 40 ( ~ f Q , )A~ 35 -40 (Kf,Q)Ab 80 Kf, Q, Ab 80 (KfyQ)Ab 80 (Kf, Q)Ab 70 -75 (Kf, Q) Ab 65 (Kf,Q)Ab 55 -60 (Kf,Q)Ab 55 (Kf,Q)Ab 50 -55 (Kf, Q) Ab 20 -25 (Kf, Q) Ab 10-15 (Kf,Q)Ab 90 -95 Kf, Q, Ab 60 (Kf, Q)Ab 30 (Kf, Q)Ab
Analcime formation
XRD
SEM
A ( 5 - 10 wt.%) (A) ( < 5 wt.%) A ( -5wt.%) A ( - 5 wt.%) A ( 5 wt.%) A ( 5 - 1Owt.%) A ( - 5 wt.%) A ( 5 - 10 wt.%) A (
-
A A A A A
-25 wt.%) -25 wt.%) (15-20wt.%) (25 - 30 wt.%) ( (
(
-3Owt.%)
A (211)>>>(100)
1- 2
A (211) >> (100)
5 2 pm
A (211)>> (100)
5 5 pm
A (211) >>>(loo)
1.5 pm
1 5 - 1Opm
e l 0 pm
/<2Opm
-
+ mordenite + albite
- 10
+ mordenite
5 pm A (211) >> (100) dissolution of analcime A (211) >> (100) A (211) >>>(loo)
5
520 pm
w W
U
304
size or both (Table 1).
3.2. Open system During alteration in the open system with dilute Na-solutions the amounts of analcime formed depend on the alkalinity of the solution as in the case of closedsystem alteration. In the 0.01N NaOH-NaC1 solution, a maximum of about 5 wt.% of analcime is formed, whereas the 0.01N NaOH solution (Table 2) leads to the formation of up to 30-40 wt.% of analcime (depending on temperature) in contrast to the reaction in closed system. The behaviour of both laumontite and albite is noteworthy. The C1solution causes a decrease of laumontite at 150°C and 200°C independent of the analcime formation thus indicating a dissolution reaction [7]. The C1-free solution, on the other hand, cause the alteration of laumontite to analcime as can be seen from the decrease of laumontite content and the corresponding increase of analcime content in the alteration products. The amount of albite remains constant at temperatures up to 200°C. At 250°C albite forms especially in the experimental run with the C1-containing solution. Scanning electron microscopy confirms the formation of albite along with analcime at 250'C. Additionally, crystallisation of mordenite is observed in the experimental run with 0.01N NaOH at 250°C. Traces of poorly crystallized smectite are formed in the entire temperature range investigated at the reaction of 0.01N NaOH + 0.01N NaC1. Investigations by SEM show the formation of smectite in alteration products formed with 0.01N NaOH, too, if the temperature was below 200°C. The morphology of analcime formed in the open system experiments is dominated by (211)- faces independent of both the reacting solution and reaction time because of the temperatures of 2 150°C.The size of analcime crystals formed in open system is larger than that of those formed in closed system at otherwise constant conditions. Crystals up to 20 pm form with 0.01N NaOH at 200' and 250°C. Furthermore, several generations of analcime are observed differing in size (Table 2). 4. CONCLUSIONS
The reacting solutions in the Smrekovec area must have been sodium dominated to cause the alteration of laumontite (and albitized plagioclase) to analcime. Analcime containing products similar to those found in nature can be formed in two different alteration processes: (1) in a closed system by reaction of concentrated alkaline saline solutions, like sea water, slightly heated by intrusive bodies and becoming alkaline by the reaction with the rock material, at low temperatures (1. 100°C); (2) by reaction in an open system with dilute sodium solutions, like either hydrothermal solutions or heated surface waters, at elevated temperatures (1. 200°C). Both sets of formation conditions could have existed at the Smrekovec volcanic complex because of its geological setting with a base in submarine conditions and a subaerial summit region.
305
Both alteration processes result in similar products consisting of analcime + phyllosilicates + albite 2 quartz f.potash feldspar. The formation of cubic analcime crystals in veins indicate low temperatures (I 100°C)of formation. Higher alteration temperatures than those favourable for analcime crystallisation cause an alteration of laumontite to albite corresponding to the observations made in the Smrekovec area. This reaction, however, needs additionally the reaction of dilute sodium solutions in an open system with high amounts of albite forming if the reacting solution is of low alkalinity. High-concentrated sodium solutions combined with elevated temperatures in closed system or dilute alkaline sodium solutions of high temperature in open systems result in formation of mordenite and analcime. The formation of the other zeolites sometimes observed at the Smrekovec volcanic complex, like clinoptilolite, heulandite, thomsonite, stilbite and yugawaralite, depend on the IUNa-ratio in case of clinoptilolite [2] and the CaINa-ratio, respectively, in case of the other zeolites [8]. REFERENCES 1. P. Kovic and N. Krosl-Kuscer, in Y. Murakami, A. Iijima and J.W. Ward (eds.), New Developments in Zeolite Science Technology, Elseveir, Amsterdam (1986) 87-92. 2. U. Barth-Wirsching and H. H(iller, Eur. J. Mineral. 1 (1989) 489-506. 3. U. Wirsching, N. Jb. Miner. Abh. 2 (1979) 193-207. 4. H. Holler, Contr. Mineral. and Petrol. 27 (1970) 80-94. 5 . J. R. Boles, Am. Mineral. 56 (1971) 1724-1734. 6. H. Abe and M. Aoki, Chem. Geol. 17 (1976) 89-100. 7. D. Savage, M. R. Cave, D. Haigh, A. E. Milodowski and M. E. Young, Eur. J. Mineral. 5 (1993) 523-535. 8. U. Wirsching, Clays and Clay Minerals 29, 3 (1981) 171-183.
299
The formation of analcime from laumontite in the Smrekovec volcanics, Northwest Slovenia - an experimental approach U. Barth-Wirsching", D. Klammef' and P. Kovic-Kraljb 'Institute of Engineering Geology and Applied Mineralogy, University of Technology Graz, Austria bGeological Survey of Ljubljana, Slovenia Summary: Analcime was formed at the expense of laumontite ,duringthe last stage of the alteration processes of the andesitic to dacitic volcanic rocks of the Smrekovec complex in Northwest Slovenia. Experimental investigations showed that this alteration is possible in either a closed system with concentrated sodium solutions, such as sea water, at low temperatures (I 100°C) or in an open system with dilute sodium solutions, such as hydrothermal solutions or heated surface waters, at elevated temperatures (r 200'C).
1. INTRODUCTION
The Upper Oligocene Smrekovec volcanic complex in Northwest Slovenia comprises an approximately 60 meters thick sequence of andesitic to dacitic rocks. These have undergone alteration processes by circulating solutions heated by rising small intrusive bodies emplaced at shallow depths [l]. Because the base of the Smrekovec volcano is assumed to be on the seafloor while the summit region probably was subaerial the reaction of different solutions was facilitated (a) concentrated solutions, i.e. seawater, (b) dilute solutions, i.e. hydrothermal or heated meteoric waters. The alteration history is rather complex and involves at least three different stages. The alteration reactions are characterized by the formation of zeolites (laumontite, mordenite, clinoptilolite, heulandite, thomsonite, stilbite, yugawaralite and analcime) and other silicate minerals, including quartz, albite, chlorite, interstratified chlorite/smectite and sphene. Among the observed zeolites, laumontite is the most common and widespread one. During the last stage of alteration laumontite - and to some extent albitized plagioclase - became instable and were altered to analcime. The formation of analcime was accompanied by changes of the interstratified chlorite/smectite minerals: the original content of the smectite component amounting to 20% and lo%, respectively, increases to 60%. Typical analcime containing alteration
300
products comprise analcime (up to 40 wt.%), interstratified chlorite/smectite, albite,
+ quartz, and 5 potash feldspar. In the most extensively altered parts quartz has been
partly or completely leached. In areas nearer to the intrusive body the alteration of laumontite to albite is observed. Besides the above-mentioned kind of analcime formation, analcime occurs in veins characterized by cube-like morphology. Till now a lot of experimental work was done on alteration reactions of various materials, like feldspars [2], nepheline [2,3,4], sodalite [4], heulandite and clinoptilolite [5], clinoptilolite tuff [6] and volcanic glasses [ 11, resulting in the formation of analcime. However, no experiments on the formation of analcime at the expense of laumontite were reported. Therefore, the aim of our experiments was to alter a rock material from the Smrekovec volcanic complex containing laumontite and albitized plagioclase into analcime containing alteration products, under conditions approaching the natural ones as close as possible, in order to investigate under what conditions the alteration may have taken place yielding products as similar as those formed in nature. 2. EXPERIMENTAL
The starting material used in the experiments had the following mineral contents: laumonite (-20 wt.%), albite (15-20 wt.%), interstratified chloritehmectite (50-55 wt.%), quartz (< 5 wt.%), potash feldspar in traces. 0.5g material of grain size < 0.09 mm (90% < 3 0 p ) were reacted with 25 ml solution of the following composition: distilled water, 0.01N NaC1,O.OlN NaOH, 0.01N CaCl,, O.lN CaC1, and solution mixtures (1:l) of 0.01N NaOH + 0.01N NaCl, 0.01N NaOH + 0.1N NaC1, 0.1N NaOH + 0.1N NaC1, 0.01N NaOH + 0.01N CaC1, and 0.01N NaOH + 0.1N CaCl,. Experiments were carried out without stirring in both closed (reaction times 20, 80,200 days) and open systems (change of solution every 20 days) in the temperature range between 50' and 250°C at autogenous pressure. All syntheses were performed twice in Teflon-coated stainless steel pressure-vessels of 70-ml capacity. The alteration reaction in a closed system is equivalent to the reaction in a closed pressure-vessel. A hydrologically open system characterized by slow percolation of solutions, that allows the addition and removal of cations to and from the reacting system, was simulated by stopping the reaction after certain periods then separating the solution from the solid followed by renewing of the solution. Reaction products were investigated by X-ray powder diffraction (XRD; Philips PW 1840, Cu-Ka radiation) and scanning electron microscopy (SEM; Cambridge Mark 2A instmment).
301
3. EXPERIMENTAL RESULTS The alteration products of the experimental runs with distilled water as well as with Ca- and Na-Ca-solutions showed that the formation of measurable amounts of analcime at the expense of laumontite and albitized plagioclase, respectively, requires a reaction with Na-dominated solutions according to the equation Ca[Al,S!40,2] * 4H2O + 2Na' + 2 Na[AlSi,O,] * H,O + Ca2' + 2H,O laumontite analcime The experimental runs with Na-solutions show that formation of analcime is possible at these conditions in both closed and open systems. In both systems analcime forms in the temperature range between 2 75' and 5 250°C. However, it is only stable up to temperatures of 5 200'C depending on the concentration of the reacting solution. At all conditions, analcime formation starts on the surface of laumontite or albite. Tables 1 and 2 show the experimental results formed at those experimental conditions yielding high amounts of analcime.
3.1. Closed system The amounts of analcime formed by alteration in closed system depend on the reacting solution. Dilute Na-solutions have to be alkaline to form noticeable amounts of analcime. The maximum amount is about 10 wt.% at the reaction of 0.01N NaOH at 200'C after 200 days. On the other hand, with a concentrated Na-solution the maximum amounts increase up to 45-55 wt.% at temperartures of 150"and 200'C after 200 days (Table 1). Accordingly, the laumontite content decreases to about 80% of the initial content in experimental runs with low-concentration solutions, whereas laumontite as well as potash feldspar and quartz disappear completely in solutions of high concentrations. Albite content decreases at all temperatures except at 250°C corresponding to the instability of analcime at this temperature. This is shown by limitations in analcime morphology formed in dilute solutions and the decreasing amount of analcime observed in the reaction products formed with concentrated solutions during increasing reaction periods (Table 1). However, the instabability of analcime in such solutions starts already at 200'C as can be seen by SEM showing residues of former analcime crystals. In addition to analcime, traces of mordenite form with highly concentrated solutions at elevated temperatures (3 150°C). Small amounts of poorly crystallized smectite are formed in the alteration products of most experimental runs at temperatures below 200°C. The morphology can be defined by the size ratio of the (100)- and (21 1)-faces which decreases with increasing temperature, reaction time, pH, and concentration of the reacting solution, respectively. Analcime with cubic morphology is formed at temperatures of 5 lOO"C, only. The size of the analcime crystals, too, is influenced by the factors mentioned above. The largest crystals 20 pm) form during the reaction in the highly concentrated solution. Additionally, several generations of analcime crystals form in this solution and differ in the size ratio of (100) to (21l), the crystal
Table 1 Analcime formation from the material used during the experimental alteration in closed system with 0.1N NaOH + 0.1N NaCl Temperature Time Lau (exp) ('C)
50 75 100 150
200
250
(days) Lau(start)
200 200 80 200 20
80 60 -70 70 10 -30 0
Yox 100
Kf, Q, Ab Kf, Q, Ab Kf,Q, Ab (Kf, Q) Ab Kf,Q,Ab
Analcime formation
SEM
XRD
(A) A (30 - 15 wt.%) A ( -40 wt.%)
80 200 20 80
A A A A
200
A (45 - 50 wt.%)
( -40 wt.%) (45 - 50 wt.%) ( -40 wt.Yo) (40 - 45 wt.%)
A (
-4Owt.%)
80
A (
-55 wt.%)
200
A (
-45
20
0
Ab
wt.%)
A (100) A (100)>> (211) A (100)>> (211) A (loo)>> (211) (211)>> (100) A (211)>> (100) A (211)>> (100) A (loo)>> (211) A (loo)>> (211) (211)>> (100) A (211) >>>(100) (211)>> (100)
-1pm
-2w -3pm
2- 3w 2- 3p
c 5 pm 1.5 pm
2- 3 5 pm 5 pm -20 pm 5 - 10 pm dissolution of analcime A (100)>> (211) 2 - 3 pm (211)> (100) -5pm A 5 pm (211)>> (100) 120 pn A dissolution of analcime
Lau (exp) : Laumontite content in the experimentally formed alteration products Lau (start) : Laumontite content in the starting material - = no analcime formation; ( ) = small amounts of a mineral; A = analcime; Kf = potash feldspar; Q = quartz; Ab = albite
-
-
+ mordenite + mordenite +mordenite
+ mordenite + mordenite
+ mordenite
W
E
Table 2 Analcime formation from the material used during the experimental alteration in open system with 0.01N NaOH Temperature Time Lau (exp) ('C)
150
200
250
(days) Lau(start) 80
100 120 140 160 180 200 20 40 60 80 100 120 140 160 180 200 20 40
60
80 75 80
% x 100
(Kf, Q) Ab (Kf,Q)Ab (Kf,Q)Ab 80 (Kf, Q)Ab 65 -70 (Kf, Q) Ab 40 ( ~ f Q , )A~ 35 -40 (Kf,Q)Ab 80 Kf, Q, Ab 80 (KfyQ)Ab 80 (Kf, Q)Ab 70 -75 (Kf, Q) Ab 65 (Kf,Q)Ab 55 -60 (Kf,Q)Ab 55 (Kf,Q)Ab 50 -55 (Kf, Q) Ab 20 -25 (Kf, Q) Ab 10-15 (Kf,Q)Ab 90 -95 Kf, Q, Ab 60 (Kf, Q)Ab 30 (Kf, Q)Ab
Analcime formation
XRD
SEM
A ( 5 - 10 wt.%) (A) ( < 5 wt.%) A ( -5wt.%) A ( - 5 wt.%) A ( 5 wt.%) A ( 5 - 1Owt.%) A ( - 5 wt.%) A ( 5 - 10 wt.%) A (
-
A A A A A
-25 wt.%) -25 wt.%) (15-20wt.%) (25 - 30 wt.%) ( (
(
-3Owt.%)
A (211)>>>(100)
1- 2
A (211) >> (100)
5 2 pm
A (211)>> (100)
5 5 pm
A (211) >>>(loo)
1.5 pm
1 5 - 1Opm
e l 0 pm
/<2Opm
-
+ mordenite + albite
- 10
+ mordenite
5 pm A (211) >> (100) dissolution of analcime A (211) >> (100) A (211) >>>(loo)
5
520 pm
w W
U
304
size or both (Table 1).
3.2. Open system During alteration in the open system with dilute Na-solutions the amounts of analcime formed depend on the alkalinity of the solution as in the case of closedsystem alteration. In the 0.01N NaOH-NaC1 solution, a maximum of about 5 wt.% of analcime is formed, whereas the 0.01N NaOH solution (Table 2) leads to the formation of up to 30-40 wt.% of analcime (depending on temperature) in contrast to the reaction in closed system. The behaviour of both laumontite and albite is noteworthy. The C1solution causes a decrease of laumontite at 150°C and 200°C independent of the analcime formation thus indicating a dissolution reaction [7]. The C1-free solution, on the other hand, cause the alteration of laumontite to analcime as can be seen from the decrease of laumontite content and the corresponding increase of analcime content in the alteration products. The amount of albite remains constant at temperatures up to 200°C. At 250°C albite forms especially in the experimental run with the C1-containing solution. Scanning electron microscopy confirms the formation of albite along with analcime at 250'C. Additionally, crystallisation of mordenite is observed in the experimental run with 0.01N NaOH at 250°C. Traces of poorly crystallized smectite are formed in the entire temperature range investigated at the reaction of 0.01N NaOH + 0.01N NaC1. Investigations by SEM show the formation of smectite in alteration products formed with 0.01N NaOH, too, if the temperature was below 200°C. The morphology of analcime formed in the open system experiments is dominated by (211)- faces independent of both the reacting solution and reaction time because of the temperatures of 2 150°C.The size of analcime crystals formed in open system is larger than that of those formed in closed system at otherwise constant conditions. Crystals up to 20 pm form with 0.01N NaOH at 200' and 250°C. Furthermore, several generations of analcime are observed differing in size (Table 2). 4. CONCLUSIONS
The reacting solutions in the Smrekovec area must have been sodium dominated to cause the alteration of laumontite (and albitized plagioclase) to analcime. Analcime containing products similar to those found in nature can be formed in two different alteration processes: (1) in a closed system by reaction of concentrated alkaline saline solutions, like sea water, slightly heated by intrusive bodies and becoming alkaline by the reaction with the rock material, at low temperatures (1. 100°C); (2) by reaction in an open system with dilute sodium solutions, like either hydrothermal solutions or heated surface waters, at elevated temperatures (1. 200°C). Both sets of formation conditions could have existed at the Smrekovec volcanic complex because of its geological setting with a base in submarine conditions and a subaerial summit region.
305
Both alteration processes result in similar products consisting of analcime + phyllosilicates + albite 2 quartz f.potash feldspar. The formation of cubic analcime crystals in veins indicate low temperatures (I 100°C)of formation. Higher alteration temperatures than those favourable for analcime crystallisation cause an alteration of laumontite to albite corresponding to the observations made in the Smrekovec area. This reaction, however, needs additionally the reaction of dilute sodium solutions in an open system with high amounts of albite forming if the reacting solution is of low alkalinity. High-concentrated sodium solutions combined with elevated temperatures in closed system or dilute alkaline sodium solutions of high temperature in open systems result in formation of mordenite and analcime. The formation of the other zeolites sometimes observed at the Smrekovec volcanic complex, like clinoptilolite, heulandite, thomsonite, stilbite and yugawaralite, depend on the IUNa-ratio in case of clinoptilolite [2] and the CaINa-ratio, respectively, in case of the other zeolites [8]. REFERENCES 1. P. Kovic and N. Krosl-Kuscer, in Y. Murakami, A. Iijima and J.W. Ward (eds.), New Developments in Zeolite Science Technology, Elseveir, Amsterdam (1986) 87-92. 2. U. Barth-Wirsching and H. H(iller, Eur. J. Mineral. 1 (1989) 489-506. 3. U. Wirsching, N. Jb. Miner. Abh. 2 (1979) 193-207. 4. H. Holler, Contr. Mineral. and Petrol. 27 (1970) 80-94. 5 . J. R. Boles, Am. Mineral. 56 (1971) 1724-1734. 6. H. Abe and M. Aoki, Chem. Geol. 17 (1976) 89-100. 7. D. Savage, M. R. Cave, D. Haigh, A. E. Milodowski and M. E. Young, Eur. J. Mineral. 5 (1993) 523-535. 8. U. Wirsching, Clays and Clay Minerals 29, 3 (1981) 171-183.