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Foster-STUDIES •. OF THE ZEOLITES-Geological Survey Professional Paper 504-D, E 

Studies of the Zeolites 

Composition of Zeolites 

of the Natrolite Group 

and 

Compositional Relations 

among Thomsonites 

Gonnardites, and 

Natrolites 

By MARGARET D. FOSTER 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 504-D, E 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1965 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretory 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

The U.S. Geological Survey Library has cataloged this publication as follows: 

Foster, Margaret Dorothy, 1895-

Studies of the zeolites. D. Composition of zeolites of the 

natrolite group. E. Compositional relations among thomsonites, gonnardites, and natrolites. Washington, U.S. Govt. 

Print. Off., 1965. 

v, 7; iii, 10 p. diagrs., tables. 30 em. (U.S. Geological Survey. 

Professional paper 504-D, E) 

Shorter contributions to general geology. 

Each part also has separate title page. 

Includes bibliographies. 

(Continued on next card) 

Foster, Margaret Dorothy, 1895-

the zeolites. 1965. (Card 2) 

Studies of 

1. Zeolites. I. Title. II. Title: Composition of zeolites of the natrolite group. III. Title: Compositional relations among thomsonites, 

gonnardites, and natrolites. (Series) 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 25 cents (paper cover) 
Studies of the Zeolites 

Composition of 

Zeolites of the 

N atrolite Group 

By MARGARET D. FOSTER 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 504-D 

Characteristic variations in composition of 

natrolites, scolecites, and mesolites, indicated 

by published analyses 

CONTENTS 

Page Page Abstract __________________________________________ _ D 1 Mesolite_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ D3 

Introduction ______________________________________ _ 1 D~cus~on_________________________________________ 5 

Natrolite _________________________________________ _ 2 References_________________________________________ 7 

Scolecite __________________________________________ _ 3 

ILLUSTRATION 

Page 

FIGURE 1. Relation between Ca(+Mg) and Na(+K) in natrolites, scolecites, and mesolites_____________________________ D6 

TABLES 

TABLES 1-4. Analyses and calculated atomic ratios of- Page 

1. N atrolite ____________________________________ ----------------------- ____________ -------------- D2 

2. Scolecite------------------------------------------------------------------------------------- 4 

3. Mesolite-------------------------------------------------------------------------------------- 5 

-4. High-N a mesolites------------------------------------------ _ __ _ __ __ __ _ _ _ _ _ _ _ ___ __ __ _ _ __ _ _ _ __ __ _ _ __ __ 5 

v 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Studies of the Zeolites 

COMPOSITION OF ZEOLITES OF THE NATROLITE GROUP 

By MARGARET D. FosTER 

ABSTRACT 

A study of the analytical data on members of the natrolite 

group of fibrous zeolites-natrolite, scolecite, and mesoliteindicates that the scolecites are most constant in composition, 

with little substitution of Mg, N a, or K for Ca, and with little 

deviation from the theoretical value in the atomic ratios for 

Ca, AI, and Si or in the molecular ratios for H20. In many 

natrolites the atomic ratio for Na, or even (Na+K), is significantly less than theoretically required, and there is often 

not sufficient Ca present to compensate for the low N a. In 

some natrolites there is some evidence of replacement of Na, 

either by Ca or by CaAl; the CaAl also replaces an equivalent 

amount of Si. In others the deficiency in Na or (Na+K) 

cannot be accounted for in these ways. Water is generally 

close to the theoretical value, despite the low N a contents. 

There is some evidence that even small amounts of Ca tend to 

increase the H20 content. 

The mesolites vary widely in Ca and N a content, but threefourths of the analyses studied are characterized by uniform and 

nearly theoretical Ca content and by variable N a content, 

which ranges from the theoretical to considerably lower than 

theoretical value. The nearly theoretical Ca, AI, and Si contents of these mesolites preclude either CaAl;::!NaSi or Ca;::!Na2 

types of substitution to explain the low N a contents. 

The very high H20 molecular ratios of several of the low N a 

natrolites and mesolites may be due to adsorbed H20 or to 

hydronium ion whose presence would compensate for the low 

Na contents. 

INTRODUCTION 

Formulas for zeolites of the natrolite group-natrolite, scolecite, and mesolite-suggest minerals of fixed 

composition. From his study of these minerals Hey 

(1932, 1933, 1936) concluded that this is true with 

respect to the ratio Si/Al, which is quite constant, and 

does not deviate notably from 1.5, but that there is 

more variation in their content of alkalies and alkaline 

earths. Most natrolites contain minor amounts of K 

and Ca; some scolecites contain minor amounts of Na 

and K; and many mesolites contain more or less Ca or 

N a than required by the formula. He found no 

evidence of NaSi~CaAl substitution, but attributed 

deviation in Na or Ca content to replacement of the 

N ~Ca type. However, a casual inspection of the 

atomic ratios of the analyses he published does not 

corroborate these conclusions as to replacement. 

Structural studies have indicated a definite relation 

and close association between the cations and the water 

molecules. Detailed study of the natrolite structure by 

Meier (1960) has shown that each Na ion is surrounded 

by 6 oxygens (4 oxygen ions and 2 water molecules), 

and each H20 molecule is close to 2 N a ions. This 

relation is expressed in the 1:1 ratio between Na ions 

and H20 molecules. Scolecite is closely related crystallographically to natrolite and the chemical composition 

is similar except that the 2 N a ions and 2 H20 molecules 

in na troli te are replaced by 1 Ca ion and 3 H20 molecules in scolecite. The mesolite formula corresponds 

compositionally to 1 molecule of natrolite plus 2 

molecules of scolecite, and the ratio of cations to water 

molecules is equivalent to 1: 1 for the N a cations plus 

1 : 3 for the Ca ions. Because of the close structural 

association between the cations and the water molecules, it would be expected that replacement of one 

cation by another or deficiency in cationic content 

would be reflected in H20 content. 

It seemed desirable, therefore, to reexamine analyses 

of these zeolites to learn the kind and extent of variation 

in composition, and the relation between variation in 

composition and H20 content. 

The analyses used in this study were carefully selected 

from the literature, particularly with respect to age, 

summation of constituents, and summation of the 

atomic ratios of the tetrahedral constituents. Analyses 

included in the study were restricted to those made 

since 1900, except where especially noted, for which 

the sum of the constituents was not less than 99.70, or 

more than 100.50, and for which the atomic ratios for 

Si and AI totaled 10±0.10. For purposes of comparsion 

all the atomic ratios for the analyses were calculated 

on the basis of 20 oxygen atoms. According to Hey's 

(1955) formulas, calculations so based give quarter-cell 

atomic ratios for natrolite and scolecite, and twelfth 

cell ratios for mesolite. 

Dl 
D2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

NATROLITE 

The 27 analyses used to study the composition of 

natrolite are given in table 1, with their atomic ratios. 

The Na20 content of these analyses ranges from a high 

of 16.73 percent to a low of 14.43 percent, or, in terms 

of atomic ratios, from Na4.n to Na3.57• K20, reported 

in about two-thirds of these analyses, ranges from 0.01 

to 0.59 percent (0.10 K atomic ratio) except in No. 26, 

which contains 1.27 percent K20 (0.20 K atomic ratio). 

In most of the analyses the atomic ratio for N a is less 

than the theoretical 4.00 indicated in the formula 

above. Even with K, the sum of the univalent cations 

(N a+ K) is less than 4.00 in about three-fourths of the 

analyses, and is 3.85 or less in about one-half of them. 

In several analyses (Na+K) is less than 3.70. 

CaO is reported in all but six of the analyses, but 

the amounts reported are generally low. Only six 

analyses reported more than 0.75 percent CaO (about 

TABLE 1.-Analyses of natrolite and their calculated atomic ratios 

[In order of decreasing Na20 content] 

Composition (percent) Atomic ratio 

H20 Positive 

No. charge 

Si02 AhOa CaO Na20 K20 H20 Total Si AI Ca Na K 

Deter- Calcu- Differmined lated ence 

------------------------------------------

1_---------------------- 46.93 27.02 16.73 9.58 100.26 5.95 4.03 4.11 4.05 4.11 -0.06 4.11 

2.---------------------- 47.09 26.99 16.46 0.01 9.80 100.35 5.97 4.03 4.04 0.00 4.14 4.04 +.10 4.04 

3----------------------- 47.1 27.1 ---ii~os- 16.4 9.44 100.04 5.96 4.04 4.02 3.99 4.02 -.03 4.02 

4_---------------------- 47.40 26.88 16.25 .11 9.67 100.36 6.00 4.01 0.00 3.98 .02 4.08 4.02 +.06 4.00 

5.---------------------- 46.95 27.06 .27 15.97 9.58 99.83 5.96 4.05 .04 3.93 4.06 4.05 +.01 4.01 

6.---------------------- 46.72 26.51 .24 15.95 .52 19.08 2 99.91 5.97 3.99 2 .05 3.95 .08 3. 79 4.18 -.40 4.13 

7----------------------- 47.32 26.30 .50 15.95 9.50 99.57 6.02 3.94 .07 3.94 4.04 4.15 -.11 4.08 

8_---------------------- 47.17 26.84 .12 15.89 .02 9.58 8 99.74 6.00 4.02 .02 3.92 4.06 3.98 +.08 3.96 

9----------------------- 47.22 27.21 15.86 .06 9. 70 100.05 5.98 4.06 3.90 4.10 3.90 +.20 3.90 

10---------------------- 47.80 26.81 15.83 9.69 100.13 6.04 3.99 3.88 4.08 3.88 +.20 3.88 

11_--------------------- 47.69 27.14 15.74 9.56 100.13 6.02 4.03 3.85 4.02 3.85 +.17 3.85 

12_--------------------- 46.91 27.10 .63 15.65 .14 4 9. 72 100.15 5.95 4.05 .08 3.85 .02 3.97 4.11 -.14 4.03 

13.--------------------- 46.38 27.36 .83 15.63 .13 9.28 99.61 5.90 4.10 .11 3.85 .02 3.94 4.20 -.26 4.09 

14.--------------------- 47.33 27.13 .10 15.63 3 9.67 99.86 6.00 4.05 .01 3.84 4.03 3.87 +.16 3.86 

15---------------------- 46.53 26.63 .44 15.53 .44 9.62 6 100.65 5.96 .4.02 6 .08 3.85 .07 4.12 4.16 -.04 4.08 

16_--------------------- 47.45 27.40 .07 15.45 .42 9.16 7100.20 5.98 4.07 .01 3. 77 .07 3.86 3.87 --.01 3.86 

17---------------------- 47.34 27.17 .48 15.42 .28 9.47 8100.17 5.98 4.04 .06 3. 77 .04 3.99 3.99 .00 3.93 

18 __ -------------------- 47.60 27.40 .13 15.36 .23 9.47 100.19 6.00 4.06 .02 3. 74 .04 3.98 3.84 +.14 3.82 

19_--------------------- 47.15 27.39 .30 15.27 .50 9.53 100.14 5.96 4.08 .04 3. 74 .08 4.02 3.94 +.08 3.90 

20---------------------- 47.38 27.63 .54 14.96 .41 9.58 100.50 5.96 4.10 .07 3.65 .06 4.02 3.92 +.10 3.85 

21_--------------------- 46.60 27.21 Trace 14.80 .31 10.24 9 99.94 5.98 4.12 3.68 .05 4.38 3. 73 +.65 3. 73 

22_--------------------- 47.33 27.67 .22 14.74 .50 9.64 100.10 5.98 4.12 .03 3.60 .08 4.06 3. 77 +.29 3. 74 

23.--------------------- 46.6 27.2 1.3 14.7 <.01 9.6 99.4 5.94 4.09 .18 3.63 4.04 4.17 -.13 3.99 

24-- -~ ------------------ 47.29 27.56 .80 14.63 .59 9.40 100.27 5.96 4.09 .11 3.57 .10 3.95 4.00 -.05 3.89 

25---------------------- 44.85 27.94 2.00 14.47 1010.68 11100.14 5. 78 4.24 .28 3.62 4.37 4.46 -.09 4.18 

26_- -------------------- 47.22 26.94 1.05 14.45 1.27 9.28 100.21 5.98 4.02 .14 3.54 .20 3.92 4.16 -.24 4.02 

27---------------------- 46.42 27.27 1.04 14.43 .47 9.64 1299.86 5.94 4.11 .14 3.57 .08 4.11 4.07 +.04 3.93 

1 Includes 0.20 H20-. 7 Includes 0.25 Fe20a. 

2 Includes 0.20 Fe20a, 0.12 MgO (0.02 Mg atomic ratio), 0.08 P205, and 0.49 insoluble. s Includes 0.01 Fe20a. a Includes O.o7 Fe20a and 0.05 MgO. o Includes 0.52 Fe20a, 0.06 FeO, 0.05 MgO, and 0.15 Ti02. • Includes 0.34 H20-. 10 Includes 0.51 H20-. 6 Includes 0.13 H20-. 11 Includes 0.20 Fe20s--FeO, c Includes 1.34 Fe20a and 0.12 MgO (0.02 atomic ratio). 12 Includes 0.59 Fe20a. 

LOCALITY AND REFERENCE FOR ANALYSIS IN TABLE 1 

1. Viagrande, Etna, Italy, Di Franco, S., 1929, Reale Accad. Lincei, Atti Cl. Sci. 

fis. mat. nat. Rend., ser. 6, v. 9, p. 660. 

2. Corporation quarry, Mount Royal, Canada, Harrington, B. J., 1905. Royal Soc. Canada Trans., v. 11, p. 25. 

3. Mount Elgon, Uganda, Udluft, Hans, 1928, Arkiv Kemi, Mineralogi och Geologi, v.9, p.2. 

4. Grosspriesen, Bohemia, Tschermak, Gustav, 1917, Akad. Wiss. Wien Math.-

Naturw. Kl., Sitzungsber. Abt. 1, v. 126, p, 544. 

5. Bohemia, Niggli, Paul, 192_; Zeitschr. Kristallographie, v. 57, p. 656~.-..analysis 9. 

6. Kola peninsula, U.s.s.R., .1:\..uz'menko, M. V., 1950, Akad. Nauk SSS.u Doklady, v. 72, p. 768. 

7. Mori, Mount Baldo, Venetiat )taly, Cavinato, Antonio, 1927, Reale Accad. 

Lincei, Cl. Sci. fis. mat. nat. Mem. ser. 6, v. 2, p. 325. 

8; Ice Valley Region, British Columbia, Canada, Phillips, A. H., 1916, Am. Jour. 

Sci., 4th ser., v. 42, p. 473. 

9. Kinbane (White Head), County Antrim, Ireland, Niggli, Paul, 1923, Zeitscbr. 

Kristallographie, v. 57, p. 656, analysis 10. 

10. Brevik, Norway, Tschermak, Gustav, 1917, Akad. Wiss. Wien Math.-Naturw. 

Kl., Sitzungsber. Abt. 1, v. 126, p. 544. 

11. San Benito, Calif., Louderback, G. D., 1909, California Univ. Dept. Geol. Bull. 

5, p. 331, analysis 23. 

12. Pokolbin, New South Wales, Australia, Anderson, C., 1904, Australian Mus. 

Recs., v. 5, p. 129. 

13. Ben Lomond, New South Wales, Australia, Anderson, C., 1906, Australian 

Mus. Recs., v. 6, p. 420. 

14. Wykertown, N.J., Milton, Charles, and Davidson, Norman, 1950, Am. Mineralogist, v. 35, p. 502. 

15. Thetford mine, eastern Quebec, Canada, Poitevin, Eugene, 1938, Toronto Univ. 

Studies, Geol. Ser., no. 41, p. 58. 

16. ValleyofChivruaiRiv~~ Lovozero massif, U.S.S.R., Vlasov, K.A., Kuz'menko, 

M. V., Es'kova, E. 1v1., 1959, Akad. Nauk SSSR Inst. Mineralog. Geokhim, 

i Kristallokhim Redkika Elementov, p. 282, Analysis 3. 

17. Amethyst Cove, Nova Scotia, Walker, T. L., and Parsons, A. L., 1922, Toronto 

Univ. Studies, Geol. ser., no. 14, p. 64. 

18. Puy de Marmant, Puy-de-Dome, France, Hey, M. H., 1932, Mineralog. Mag. v. 23..t.. p. 246, analysis 1. 

19. Cape .Hlomidon, King's County, Nova Scotia, Hey, M. H., 1932, Mineralog. 

Mag. v. 23, p. 246, analysis 5. 

20. Salesel, Leitmeritz, Bohemia, Hey, M. H., 1932, Mineralog. Mag. v. 23, p. 246, 

analysis 2. 

21. Vrahozily ( =Frauschile), nr. Boreslau., S.E. ofTeplits-Schonau, Bohemia, NovaCek, Radim, 1936, Praha, Narodnr Mus. Casopis, v. 110, p. 50. 

22. Rhiw, Camarvonshire, Scotland, Hey, M. H., 1932, Mineralog. Mag. v. 23, p. 

246, analysis 4. 

23. Red Island, Hawkes Bay, North Island, New Zealand, Mason, Brian, 1955, 

New Zealand Jour. Sci. and Technology, sec. B, v. 36, p. 558. 

24. De Beers diamond mine, Kimberley, South Africa, Hey, M. H., 1932, Mineralog. 

Mag., v. 23, p. 246, no. 6. 

25. Highwood Mountains, Mont., Larsen, E. S., Hurlbut, C. S., Jr., Griggs, David, 

Buie, B. F., and Burgess, C. H., 1941, Geol. Soc. America Bull., v. 52, p. 1852. 

26. Snake Hill, North Bergen, N. J., Hey, M. H., 1932, Mineralog. Mag. v. 23, p. 

246, no. 8. 

27. Budllany, S. W. of Praha, Bohemia, Kratochvfi, Franti;ek, 1933, Praha Narod. 

nfho Mus. 6asopis, v. 107, p. 42. 
COMPOSITION OF ZEOLITES OF THE NATROLITE GROUP D3 

0.10 Ca atomic ratio), and only one reported as much 

as 2.00 percent CaO (0.28 Ca atomic ratio). Several 

of the higher CaO values were reported in analyses 

significantly deficient in N a20, and thus raised the 

cationic content. However, little or no CaO was 

reported in several analyses that were significantly 

deficient in N a20 ( + K20). 

The Si and Al atomic ratios are generally 6.00 ±0.10 

and 4.00±0.10, respectively. Only one analysis, No. 

25, yields a Si atomic ratio with a greater deviation, 

-0.22. Deviations in AI content greater than 0.10 

are slightly more common, being found in four analyses. 

The greatest deviation, +0.24 is in analysis No. 25. 

The atomic ratios for Si, Al, N a, and Ca in No. 25 

indicate a slight CaAl replacement of NaSi. This 

type of replacement is also indicated in No. 13. Ca 

replacement of N ~( + K2) is indicated in No. 23, and 

No. 26. A little of both types may be suggested by 

the atomic ratios of Nos. 12 and 27. In most of the 

analyses, however, the atomic ratios for Ca are so low, 

and the Si and Al ratios are so close to the theoretical 

values that the low Na ratios cannot be explained by 

either type of replacement. 

The H20 content of these natrolites is very constant 

and very close (±0.15) to the theoretical 4.00 in 24 of 

the 27 analyses, even though (Na+K) is more than 

0.20 deficient in one-third of the analyses. For some 

of the analyses that are low in N a but for which the 

atomic ratio of H20 is near 4.00 or even higher, the 

H20 value can be accounted for if the Ca present is 

considered as contributing to the H20 content in the 

3:1 ratio as in scolecite. In No. 27, for example, the 

atomic ratio for (N a+ K) is only 3.65, and consequently, 

accounts for a H20 molecular ratio of only 3.65 H20. 

However, ..tR-e atomic ratio of Ca, 0.14, tripled (0.42) 

and added to 3.65 gives a calculated H20 ra.tio of 4.07, 

compared to the determined value of 4.11. Other 

analyses in which the atomic ratio for (Na+K) is much 

lower than the H20 molecular ratio and for which it is 

necessary to include the Ca value tripled to obtain a 

calculated H20 value comparable to the determined 

value are Nos. 17, 20, 24, and 25. This suggests that 

Ca is an intrinsic constituent of these natrolites. In 

other analyses, as in No. 26, inclusion of the Ca tripled 

in the calculated water computation yields a H20 value 

that is somewhat higher than the determined value, 

suggesting that some, at least, of the Ca may be 

extraneous to the natrolite molecule. In other analyses, 

as in No. 21, the determined water is considerably 

higher than the calculated. This analysis reports no 

Ca. Such a high H20 content may be due to adsorption 

of H20 in a humid atmosphere by the finely ground 

sample before analysis, H20- being seldom reported 

in analyses of zeolites, or a high H20 content may be 

71431-604-64-2 

due to the presence of hydronium ions, which would 

compensate for the low Na content. 

SCOLECITE 

CauA4.oSio .o020·6.0 H30 

The 16 analyses used to study the composition and 

water content of scolecite are given in table 2, together 

with their atomic ratios calculated on the basis of 20 

oxygen atoms. The CaO content of these analyses is 

quite constant, ranging only between 13.58 and 14.86 

percent. The corresponding atomic ratio for Ca ranges 

only between 1.89 and 2.09, or 2.0±0.11. MgO is 

reported in only four of the analyses. The highest 

amount is only 0.32 percent or an atomic ratio for Mg 

of only 0.06. Na20 was reported in one-half of the 

analyses, most of which also reported K20. However, 

the amounts found were low, and the highest atomic 

ratio for (N a+ K) in any of the analyses was only 0.20. 

For most of the analyses the atomic ratios for Si and 

AI were within 0.10 of the theoretical 6.00 and 4.00, 

respectively. As these values and those for Ca are so 

close to the theoretical, there is little indication of 

replacement except in analyses 14, 15, and 16, in 

which the atomic ratios for Ca are the lowest and those 

for (Na+K) the highest. In No. 15 the atomic ratio 

for (Na+K), 0.20, and the deficiency in the atomic 

ratios for Ca, 0.08, suggest slight replacement of Ca by 

(N a+ K)2. The deviation in the atomic values of 

No. 15 for Si and Al of -0.12 and +0.14, respectively, 

would suggest CaAl replacement for NaSi if the Ca 

were not already lower and the N a higher than the 

theoretical values. In Nos. 14 and 16 replacement is 

of the N a2 --?Ca tVI>e. 

The molecular ratios for H20 for all the analyses are 

within 0.20 of the theoretical value except for No. 2, 

for which H20 is low, 5.71, and No.6, for which H20 is 

high, 6.32. However, the high H20 molecular value in 

No. 6 can be partially accounted for if H20 equivalent to 

N a is added to the tripled Ca value. Molecular values 

of H20, calculated on the basis of a 1:3 relation between 

Ca atoms and H20 molecules and 1 : 1 relation between 

Na atoms and H20 molecules, agree fairly well with the 

determined H20 molecular ratios. For analyses 15 

and 16, as well as for No. 6, it is necessary to include 

H20 equivalent to the (N a+ K) present to produce a 

calculated H20 value more nearly approximating the 

determined H20 value. 

MESO LITE 

N a1.33Ca1.3aAl4 .oSio .o02o·5. 33 H20 

Analyses of 17 mesolites, together with their atomic 

ratios calculated on the basis of 20 oxygen atoms, are 

given in table 3. For 13 of the 17 analyses, Nos. 4-16, 

the atomic ratio for Ca is close to the theoretical value 
D4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

TABLE 2.-Analyses of scolecite and their calculated atomic ratios 

[In order of decreasing CaO content] 

Composition (percent) Atomic ratio 

No. 

Si Al Ca Mg Na K De- Cal- Difierterm.ined culated ence 

-----1----------------------------------------------

l_ ________________ 45.16 25.90 14.86 ---o:os· 0.16 0.06 13.66 99.80 5. 94 4.01 2.09 0.04 o.oo 5.99 6.31 -0.32 

2----------------- 45.22 27.25 14.67 Trace None 13.20 100.42 5.86 4.16 2.04 0.00 .00 .00 5. 71 6.12 -.41 

a ______ ----------- 45.9 26.26 14.63 -------- -------- -------- 13.77 100.56 5.97 4.02 2.04 -------- -------- -------- 5.97 6.12 -.15 4 _____ ------------ 45.00 26.77 14.50 -------- -------- -------- 13.67 99.94 5.89 4.13 2.03 -------- -------- -------- 5.97 6.09 -.12 

5 _____ ------------ 47.08 25.16 14.59 -------- -------- -------- 113.40 100.23 6.11 3.84 2.02 -------- -------- -------- 5.80 6.06 -.26 

6 _____ ------------ 45.56 25.70 14.23 .50 .11 14.43 100.53 5.98 3.98 2.00 .13 .02 6.32 6.15 +.17 

7----------------- 46.10 26.32 14.22 .12 13.60 100.36 5.98 4.02 1. 98 ----:oif .03 5.89 5.97 -.08 

8 ____ ------------- 46.10 25.05 14.17 .32 .03 213.91 3100.13 6.06 3.88 1.99 .00 6.05 6.15 -.10 

9 ____ ------------- 45.59 26.25 14.10 .19 .33 .04 13.99 100.49 5.95 4.04 1.97 .04 .09 .00 6.09 6.12 -.03 

10 _______ --------- 46.40 26.69 14.10 -------- -------- -------- 13.53 100.72 5.98 4.06 1.95 -------- -------- -------- 5.82 5.85 -.03 

ll ______ ---------- 45.71 26.87 14.08 -------- -------- -------- 13.88 100.54 5.94 4.11 1.96 -------- -------- -------- 6.01 5.98 +.03 12 ________________ 46.17 25.83 13.96 .12 -------- -------- 13.88 99.96 6.03 3.97 1. 95 .02 -------- -------- 6.05 5.91 +.14 

13 ____ ------------ 45.96 26.10 13.91 -------- -------- -------- 13.97 99.94 6.01 4.02 1. 95 -------- -------- -------- 6.10 5.85 +.25 14 ____ ------------ 45.78 26.23 13.66 • 70 .11 13.44 4 99.99 5.97 4.03 1. 91 .18 .02 5.85 5.93 -.08 

15 _________ ------- 44.63 26.68 13.63 .66 .18 13.50 99.28 5.88 4.14 1. 92 .17 .03 5.94 5.96 -.02 

16 _____ ----------- 46.37 25.80 13.58 .64 .13 13.84 100.36 6.04 3.96 1.89 .16 .02 6.02 5.85 -.17 

1 Ignition loss. a Includes 0.55 Fe20a. 

2Includes 0.13 H20-. ' Includes 0.07 FeaOs. 

LOCALITY AND REFERENCE FOR ANALYSES IN TABLE 2 

1. Syhadree Mountains, Bombay, India, Hey, M. H., 1936, Mineralog. Mag. v. 24, p. 229, no. ~ B.M. no. 33887. 

2. Nr. Azhar, vaucasus, USSR, Shkabara, M. N., 1948, Akad. Nauk SSSR 

Doklady, v. 63, p. 730. 

3. Teigarhorn, Berufjord, Iceland, Cavinato, Antonio., 1927, Reale Accad. Lincei, 

Cl. Sci. fls. mat. nat. Mem. ser. 6, v. 2, p. 331. 

4. Maderanerthal, Switzerland, Cavinato, Antonio., 1927, Reale Accad. Lincei. 

Cl. Sci. fis. mat. nat. Mem. ser. 6, v. 2, p. 331. 

5. Teigarhorn, Iceland, Koizume, Mitsue, 1953, Mineralog. Jour. Japan, v. 1, p. 39. 6. Valle di Viu, Valle di Lanzo, Italy, Gennaro, Virginia, 1929, Reale Accad. Sci. 

Torino Atti, v. 64hp. 141. 7. Poonah, India, Tsc ermak, Gustav, 1917, Akad. Wiss. Wien Math-naturw. Kl. 

Sitzungsber. Abt. I, v. 126, p. 544. 

8. An Gearna, Mull, Scotland, M'Lintock, W. F. P., 1915, Royal Soc. Edinburgh 

Trans, v. 51, p. 5. 

of 1.33, being 1.33±0.07. In the other four, Ca is 

about 0.20 higher than theoretical value in three, 

(Nos. 1, 2, and 3), and 0.12 lower in one, (No. 17). 

In the three analyses in which Ca is high, N a is low; 

in No. 17, in which Ca is low, Na is high. In this last 

analysis the relation between Ca and N a can be interpreted as replacement of 0.12 Ca by 0.22 Na, but the 

relations between Ca and N a and between Si and AI in 

Nos. 1, 2, and 3, do not permit such an interpretation. 

In the group of 13 in which Ca is very constant and close 

to the theoretical value, the amount of Na present varies 

considerably, and in most is deficient. However, 

because of the fact that several contain a little K, or 

that Ca is slightly greater than the theoretical 1.33, 

the cationic charge is 4.00±0.10 for more than half of 

these analyses. In the analyses for which the positive 

charge is less than 3.90, slight adjustments in the 

amounts of Si and AI present produce the lower negative 

charges that just balance the lower positive charges. 

The Si ratio is 6.00±0.10 for all the analyses given 

in table 3, and the AI ratio is 4.00:!:0.10 for all but two, 

Nos.10 and 14, in whichitis4.11 and4.16, respectively. 

However, as the respective Si ratios for these analyses 

are not low by similar amounts, replacement of the 

CaAl~NaSi type is not indicated. Nor is similar 

9. AlomatA, Eritrea, Italy, Scherillo, Antonio, 1938, Periodico Mineralogia, Roma, v. 9.J p. 68. 

10. Dry Lake, Clark County, Nev., Gi::tnella, V. P., and Hedquist, Wilber, 1942, 

The Mineralogist, Portland, Oreg., v. 10, p. 108. 

11. Teigarhorn, Iceland, Koizum.i, Mitsue, 1953, Mineralog. Jour. Japan, v. 1, p. 39. 

12. Teigarhorn, Iceland, Bauer, Jaroslav, and Malkova, Ludmila, 1959, Sci. Papers Inst. Chern. Technology, Prague, p. 72. 

13. Miage, Monte Bianco, Italy, Cavinato, Antonio, 1927, Reale Accad. Lincei, 

CI. Sci. fls. mat. nat. Mem., ser. 6, v. 2, p. 331. 

14. Digby Gut, Annapolis County, Nova Scotia, Walker, T. L., and Parsons, A. L., 

1922, Toronto Univ. Studies, Geol. Ser. no. 14, p. 68. 

15. Valle di Viu, Valle di Lanzo, Italy, Gennaro, Virginia, 1929 ,Reale Accad. Sci. 

Torino Atti, v. 64, p. 141. 

16. Bettolina Pass, Valle di Ayas, Monte Rosa, Italy, Gennaro, Virginia, 1929, Reale 

Accad. Sci. Torino Atti, v. 64, p. 137. 

replacement, or the reverse, except in a very slight 

degree, perhaps, indicated in any of the other analyses 

because of the close agreement of the Si and AI ratios 

with the theoretical value. 

For most of the analyses the determined H20 values 

yield molecular ratios that agree fairly w~ with the 

the theoretical values. Furthermore, molecular H20 

ratios calculated on the basis of a 1 : 1 relatio.1 between 

N a(+ K) ions and H20 molecules, and a 1 :3 relation 

between Ca ions and H20 molecules, agree within 0. 20 

molecule with the H20 ratios based on the determined 

H20, except for analyses Nos. 9, 14, and 16. For Nos. 

9 and 14, the determined H20 ratios are very high, 5.77 

and 5.85, respectively. For No. 16 the determined 

H20 ratio is only 5.42, quite close to the theoretical5.33, 

but it is much higher than the calculated H20 because 

of the low Ca and Na content of this sample. Na is 

also low in Nos. 9 and 14. The high H20 content 

reported for these analyses may be due to hydronium 

ion, whose presence would compensate for their low 

Na content. On the other hand, these high H20 

values may be due to adsorption of H20 before analysis 

by the finely ground specimen in a humid environment. 

In most of these analyses only total water was reported: 

H20- and H20 + were differentiated only in analysis 
COMPOSITION OF ZEOLITES OF THE NATROLITE GROUP D5 

TABLE 3.-Analyses of mesolite, and their calculated atomic ratios 

[In order of decreasing CaO content] 

Composition (percent) 

No. 

CaO Total I 

Si Al 

Atomic ratio 

Ca Na K 

Charge 

Positive Negative Deter- Calcu- Differmined lated ence 

---------------------------------- 1 _____ ---------------- 44.96 26.30 11.15 4.10 13.20 99.71 5.90 4.07 1. 57 1.04 5. 78 5. 75 +0.03 4.18 4.19 2 _____ ---------------- 44.40 25.63 10.97 5.02 13.93 99.95 5.90 4.01 1.56 1.29 6.17 5.97 +.20 4.41 4.37 

a _____ ---------------- 45.66 26.11 10.90 4.46 (1) 100.66 5.95 4.01 1.52 1.13 15.88 5.69 +.19 4.17 4.17 4 ________ ------------- 45.97 27.00 10.10 4.98 12.78 100.83 5.92 4.10 1.39 1. 24 5.49 5.41 +.OS 4.02 4.02 

5 ________ ------------- 47.13 26.02 10.09 4.50 0.11 12.17 100.02 6.06 3.94 1.39 1.12 0.02 5.22 5.31 -.09 3.92 3.94 

6 _______ -------------- 46.98 26.43 10.06 4. 57 .05 11.94 100.03 6.03 3.99 1.38 1.13 5.11 5.27 -.16 3.89 3.91 

7--------------------- 46.05 26.84 10.00 3.82 . 79 12.30 99.80 5.96 4.09 1. 39 .96 .13 5.31 5.26 +.05 3.87 3.89 g _____ ---------------- 46.01 26.66 9.88 4.66 .20 12.69 2100.48 5.97 4.07 1. 37 1.17 .03 5.49 5.31 +.18 3.94 3.91 

9 _________ ------------ 46.08 26.64 9.86 4. 20 13.30 100.08 5.99 4.08 1.37 1. 05 5. 77 5.16 +.61 3. 79 3.80 

10 ____ ---------------- 46.15 27.04 9. 73 4.64 .06 12.36 99.98 5. 96 4.11 1.34 1.16 5.32 5.18 +.14 3.84 3.83 

ll_ _____ - ------------- 46.50 26.58 9. 72 4.97 12.29 100.06 5.99 4.04 1. 34 1.24 5.28 5.26 +.02 3.92 3.92 12 ____ ---------------- 46.04 26.32 9. 72 5. 32 .40 12.48 100.28 5. 96 4.02 1.35 1.34 .06 5.39 5.45 -.06 4.10 4.10 

13 ____ ---------------- 45.97 25.98 9.69 4. 79 -------- 313.38 99.81 6.01 4.00 1.36 1.22 5.25 5.30 -.05 3.94 3.96 14 ____ ---------------- 45.70 27.16 9.67 4.24 (4) 100.13 5.94 4.16 1.35 1.07 '5.85 5.12 +.73 3. 77 3. 76 15 ______ -------------- 46.71 26.45 9.35 5.33 .11 12.56 100.51 6.01 4.01 1.29 1.33 .01 5.39 5.21 +.18 3.92 3.93 

16 _________ ----------- 46.44 26.86 8.84 4.60 .32 12.67 5 99.93 6.00 4.09 51.26 1.15 .05 5.42 4.98 +.44 3. 72 3. 73 

17-------------------- 46.17 26.88 8. 77 6.19 12.16 100.17 5.95 4.08 1. 21 1. 55 5.23 5.16 +.07 3.97 3.96 

1 Ignition loss, 13.53. • Ignition loss, 13.36. 2 Includes 0.38 Fe,Oa (FeB+ atomic ratio=0.04). 5 Includes 0.20 MgO (Mg atomic ratio=0.04). a Includes 1.34 H,o-. 

LOCALITY AND REFERENCES FOR ANALYSES IN TABLE 3 

1. Berufjord, Iceland, Cavinato, Antonio, 1927, Reale. Accad. LinceCCl. Sci. 1is. mat. nat. Mem., Roma, ser. 6, v. 2, p. 339. 

2. Kalageran, S. of Tiflis, USSR., Tvalchrelidze, A. A., 1922, Univ. Tillis Bull. no. 2, p. 154. Mean of 4 analyses. 

3. Kilpatrick, Dumbartonshire, Scotland, Koizumi, Mitsue, 1953, Mineralog. Jour. Japan v. 1, p. 39. 

4. Nishishioda-mura, Nagano Pref., Japan, Koizume, Mitsue, 1953, Mineralog. Jour. Japan, v. 1, p. 39, no. 15. 

5. Iceland, Hey, M. H., 1933, Mineralog. Mag. v. 23, p. 423, no. 2. 6. Syhadree Mountains, Bombay, India, Hey, M. H., 1933, Mineralog. Mag., v. 23, p. 423, IW. 3. 7. Bhore Ghaut, Syhadree Mountains, Bombay, India, Hey, M.H., 1933, Mineralog. Mag.t v. 23, p. 423, no. 1. 

8. Cape a'Or, Nova Scotia, Walker, T. L., and Parsons, A. L., 1922, Toronto Univ. studies, Geol. Ser., no. 14, p. 58, no. 1. 

13. If the value for total water had been used to 

calculate the determined H20 molecular ratio for No. 

13, the H20 ratio would have been 5.84, instead of 5.25, 

the value Dbtained when the H20+ value was used :in 

the calculation. Thus H20 ratios based on total H20 

values may be high because of adsorbed water. 

TABLE 4.-Analyses of high-Na mesolites 

PERCENT 

-------·1--------------------- l ______ ----------------- 40.03 27.88 6.03 10.05 0. 40 1 11. 10 2 100 .. 29 2 ______ ----------------- 41.15 29.49 5.33 11.02 

3 --------------------- 40.59 29.69 5.06 11.00 . 25 13. 52 100. 76 • 51 13. 58 100. 43 

ATOMS PER TWELFTH CELL 

Si AI Ca(+Mg) Na(+K) H20 

----------1--------------------

1_ ----------------------------- 2_ -----------------------------

3------------------------------

1 Includes 3.12 H20-. 

5.48 

5.45 

5.41 

4.50 

4.60 

4.66 

0.92 

. 76 

.72 

2. 73 

2.86 

2.92 

2 Includes 0.85 Fa,oa, 0.59 FeO, 0.22 MgO (0.04 atomic ratio), and 0.02 Ti02• 

5.07 

5.97 

6.03 

1. Rio Cambone, Montiferro, Sardinia, Deriu, M. 1954, Periodico Mineralogia Roma, v. 23, p. 42. 

2. and 3. Kladno, Bohemia, Antonin, Rudolf, 1942, Kralovske Cesk~ Spoleenoste Nauk, Vestntk Art. 2, p. 11. 

9. Berufjord, Iceland.~.. Cavinato, Antonio, 1927, Reale Accad. Lincei Cl. Sci. fis. mat. nat. Mem . .11.oma, ser. 6, v. 2, p. 339. 

10. Kvivig, Stroma, Faroe Islands, Hey, M. H., 1933, Mineralog. Mag. v. 23, p. 423, 

no.4. 

11. Faroe Islands, Giirgey, R., 1909, Tschermaks Mineralog. Petrog. Mitt. v. 28, p. 95. 

12. Nova Scotia, Walker, T. L., and Parsons, A. L., 1922, Toronto Univ. Studies, 

Geol. Ser., no. 14, p. 58, no. II. 

13. Ostero, Faroe Islanq_s..! Clarke, F. W., 1910, U.S. Geol. Survey Bull. 419, p. 285, B. 14. Nishishioda-mura, .Nagano Pref., Japan, Koizumi, Mitsue, 1953, Mineralog. Jour. Japan, v. 1, p. 39, no. 14. 

15. Poonah, Bombay, India, Bowman, H. L., 1909, Mineralog. Malb v. 15, p. 220. 

16. Yastreb, near Kurdjali, Bulgaria./. Ko.stov, Ivan, 1958, Sofia univ., Biolog.- Geolog.-Geograph. Fakultet, Gomshmk v. 53, p. 3, no. 4. 

17. North Table Mountain, Golden, Colo., Clarke, F. W., 1910, U.S. Geol. Survey 

Bull. 419, p. 285, A. 

Three analyses of high Na mesolite are shown in table 

4. These analyses are very similar to each other but 

very different from the mesolite analyses given in table 

3, being respectivley lower in Si and Ca, and higher in 

AI and N a. Such compositions as indicated by these 

analyses cannot be derived from theoretical mesolite 

by either NaSi+=±CaAl or Na2¢Ca replacement. They 

can only be derived from mesolite by replacement of 

an average of about 0.55 CaSi by 0.55 N a3Si. These 

analyses are very similar to some of the analyses of 

gonnardite published by Meixner, Hey, and Moss (1956) 

and by Kostov (1958), and to some high-Na thomsonites 

published or cited by Hey (1932). Such compositions 

can be derived from thomsonite by a combination of 

N ~Ca and N aSi--?CaAI replacement. 

DISCUSSION 

The most significant finding resulting from this study 

of analyses of the natrolite group of zeolites is that the 

amounts of Si, AI, and Ca present usually agree very 

well with the amounts required by the formulas but 

that the amount of Na present is often deficient. As 

a consequence, scolecites are the most uniform in com-
D6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

0 

i= 

<( 

0:: 

() 

2.4 

2.0 

f~ 1.6 ~ Ideal mesolite 

~ . { ~*. . ~ 

~ 

~ High-Na 

~ 1.2 

0 

~ 

<( 

ro 

~ ~esolite 

~ ·.'1 

~ Ideal nat\olite 

() 

0:8 

0.4 

~ 

~~ • 

2.0 0 0.4 0.8 1.2 1.6 2.4 2.8 3.2 3.6 4.0 

Na ATOMIC RATIO 

FIGURE 1.-Relation between Ca( + Mg) and N a(+ K) in natrolites, scolecites, and mesolites. 

position and conform most closely with the requirements of the formula, and natrolites deviate most from 

the requirements of the formula. In mesolites the Ca 

is usually close to the theoretical value, but the Na is 

often significantly lower than the theoretical value. 

As the other constituents deviate so little from the 

theoretical, the deficiency in N a cannot be interpreted, 

generally, in terms of either type of replacement, 

Ca--?Na2 or CaAl--?NaSi. In some natrolites there 

is sufficient Ca or K present to produce a positive 

cationic charge close to the theoretical 4.00. In some 

mesolites also theCa, although close to the theoretical, 

is enough higher to bring the positive charge close to 

4.00. However, in other natrolites and mesolites the 

positive cationic charge is only 3.75, or even less. 

Slight adjustments in the amounts of Si and AI present 

produce the lower negative charges that just balance 

the lower positive charges. 

The relation between Ca and Na in these zeolites is 

shown graphically in figure 1. The points representing 

the relation between Ca and Na in scolecites all fall in 

a very small area closely grouped around the point 

representing ideal scolecite, whereas the points representing the relation between Ca and N a in mesolites and 

natrolites are more scattered. Most of the points 

representing the relation between Ca and N a in analyses 

of mesolites and natrolites fall left of the points representing ideal mesolite and ideal natrolite, respectively, 

thus indicating lower N a than ideally presumed to be 

present. However, three points representing the relation between Ca and N a in samples of high N a mesolite 

fall lower and far to the right of the mesolite area; 

closer to the natrolite area than to the me8olite area. 

In composition these analyses resemble gonnardites or 

high-N a thomsonites rather than mesolites. 

Most H20 molecular ratios based on reported H20 

contents are close to the theoretical value specified in 

the formula. Also, most of the H20 values calculated 

from the Ca( + Mg) and N a(+ K) present agree within 

0.20 molecule of the H20 values based on the amount of 

H20 reported in the analysis. In general the determined H20 ratios are higher than the calculated ratios. 

A few determined H20 values are very high. As most 

zeolite analyses report only total H20, and do not 

differentiate H20- and H20+, these higher values for 

determined H20 may be due to adsorbed H20, which is 

probably very slight in most of the samples analyzed 

but in some may be considerable, and so produce an 

unrealistically high H20 content particularly if the 

finely powdered sample has been in a hunlid environment before analysis. The dehydration curves of 

Koizumi (1953) and Peng (1955) indicate that H20 
COMPOSITION OF ZEOLITES OF THE NATROLITE GROUP D7 

that is an intrinsic part of the structure does not begin 

to come off below about 150° 0; consequently determination of H20- at 110° 0 is perfectly feasible. 

It is therefore recommended that H20- be routinely 

determined in the zeolites. 

The highest H20 values in both the natrolites and the 

mesolites occur in analysis that are very low in Na and 

that have the lowest positive charges. It may be, 

therefore, that these high H20 values are caused by 

hydronium ions which compensate for the low cationic 

content of the zeolite. 

REFERENCES 

Hey, M. H., 1932, Studies on the zeolites. Part III. Natrolite 

and metanatrolite: Mineralog. Mag., v. 23, p. 243-289. 

---1933, Studies on the zeolites. Part V. Mesolite: Mineralog. Mag., v. 23, p. 421-447. 

---1936, Studies on the zeolites. Part IX, Scolecite and 

metascolecite: Mineralog. Mag., v. 24, p. 227-253. 

---1955, An index of mineral species and varieties arranged 

chemically, 2d ed.: London, British Museum (Natural 

History), 728 p. 

Koizumi, Mitsue, 1953, Studies on water in minerals. Part I. 

The differential thermal analysis curves and the dehydration 

curves of zeolites: Mineralog. Jour. Japan, v. 1, p. 36-47. 

Kostov, Ivan, 1958, Zeolites in Bulgaria: scolecite, mesolite, 

"gonnardite," and thomsonite: Sofia Univ. Biolog.-

Geolog.-Geograph. Fakultet, Godishnik, v. 53, p. 1-24. 

Meier, W. M., 1960, The crystal structure of natrolite: Zeitschr. 

Kristallographie, v. 113, p. 43Q-444. 

Meixner, Heinz, Hey, M. H., and Moss, A. A., 1956. Some new 

occurrences of gonnardite: Mineralog. Mag., v. 31, p. 265-

271. 

Peng, C. J., 1955, Thermal analysis study of the natrolite group: 

Am. Mineralogist, v. 40, p. 834-856. 

Taylor, W. H., Meek, C. A., and Jackson, W. W., 1933, The 

structures of the fibrous zeolites: Zeitschr. Kristallographie, 

v. 84, p. 373-398. 

Studies of the Zeolites 

Compositional 

Relations among 

Thomsonites 

Gonnardites 

and N atrolites 

By MARGARET D. FOSTER 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 504-E 

Relations among thomsonites, high-sodium thomsonites, gonnardites, high-sodium mesolites, and 

natrolites as indicated by published analyses 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Studies of the Zeolites 

COMPOSITIONAL RELATIONS AMONG THOMSONITES, GONNARDITES, 

AND NATROLITES 

By MARGARET D. FosTER 

ABSTRACT 

A study of post-1885 analyses of thomsonite selected from 

Hey's 1932 compilation confirms the isomorphous series between 

thomsonite and faroelite. This isomorphous series, which is 

characterized by replacement of CaAl by NaSi, was recognized 

by Winchell (1925, 1926) and Hey (1932). Hey's formula 

for gonnardite is related to thomsonite in the same way and 

carries this line of replacement a step beyond faroelite. However, the total number of cations, and the relation between 

Si and AI and Ca and N a in analyses of gonnardite, including 

those published by Meixner, Hey, and Moss (1956) indicate replacement of Ca by N a2 as well as replacement of Ca as CaAI 

by NaSi. Similar numbers of total cations, and similar relations between Si and AI and Ca and N a were also found in some 

analyses of high Na thomsonites and in high Na mesolites. 

Plotted points representing the relation between Ca and N a 

in these analyses fall, not along the thomsonite-faroelite line, 

but along a line representing dual replacement, to the same 

degree, of Ca by N ~ and of CaAl by NaSi. Such dual replacement of Ca in thomsonite leads theoretically to natrolite: 

Thomsonite: Ca2.oNa1.0Al5.oSi5.o02o·6.0 H20 

Ca1.0N auA4.sSiu02o·5.0 H20 

~atrolite: Ca.oNauAI,..oSi6.0020·4.0 H20 

The analyses alone suggest an isomorphous series between 

thomsonite and natrolite, with gonnardite as the intermediate 

member. 

For such a series only formulas indicating ranges of composition are adequate. As there appears to be no natural hiatus 

in composition between thomsonite and gonnardite, the division was arbitrarily fixed at the point where Ca and N a are 

equal. The suggested range formulas for the series are: 

Thomsonite: Nal.0-1.6Ca2.0-1.6Ais.o-uSio.o-5.202o·6.Q-5.6 H20 

Gonnardite: N au-3.4Cau-D.4Alu-4.2Sis.2-s.s020·5.6-4.4 H20 

Natrolite: Nau-uCao.4-o.oAlu-4.oSio.s-6.o02o·4.4-4.0 H20 

Although thomsonite and natrolite have similar aluminosilicate frameworks, they differ considerably in detail. Thus 

there may be a structural hiatus between thomsonite and natrolite like that between muscovite and lepidolite. No study 

has been made of the structure of gonnardite. The indices of 

refraction of gonnardite are intermediate between those of 

thomsonite and natrolite, those of thomsonite the higher, and 

those of natrolite the lower. However, the optic sign of gonnardite is negative, and those of thomsonite and of natrolite 

are positive. 

INTRODUCTION 

The formulas for thomsonite and gonnardite, like 

those for natrolite, mesolite, and scolecite, suggest 

minerals of fixed and definite composition, although 

they are well known to be quite variable in composition. 

Winchell (1925) recognized that there is isomorphoug 

N aSi+=ZCaAI replacement in thomsonite, as between 

thomsonite, Ca2 .oN a1.oAls .oSis. 002o ·6.0 H20 and 

Ca1.2sN ausAI4.2sSi5.7s02o·5.0 H20. Hey (1932) concurred 

with this view but considered that there is also considerable N ~Ca replacement, which Winchell had 

considered unimportant. However Hey's formula for 

gonnardite, 2[Na2CaAI4Si602o·7H20], is related to thomsonite by NaSi---?CaAI replacement only, although 

atomic ratios derived from analyses of gonnardite, 

including those published by Meixner, Hey, and 11oss 

(1956), indicate both NaSi---?CaAI and Na2---? Ca substitution. 

The relation between H20 and the cations in thomsonite is less simple than in natrolite or mesolite. 

Taylor, Meek, and Jackson (1933) assume the environment of the N a ion and one of the Ca ions to be similar 

to that of the Na in natrolite, except for an additional 

H20 molecule that increases the coordination from sixfold to sevenfold with 4 oxygen ions and 3 water molecules. The other Ca ion they assume to be in eightfold coordination, with 6 oxygen ions and 2 water 

molecules. The relation between water molecules and 

cations is as though there were 1 water molecule for 

each N a ion, 2 for one-half of the Ca ions and 3 for the 

other half, or an average of 2.5 to 1 for all theCa ions. 

The water content of gonnardite seems to be in doubt. 

Hey.(1955) _gives.the.formula as2[ Na2CaA14Si6020 ·7H20], 

but in 1956 Meixner, Hey, and Moss give the formula as 

[(Ca,Na)G-s(Si,Al)200 40 ·12 H20], and Deer, Howie, and 

Zussman (1963 p. 359) give the formula as 

Na2Ca[(Al,Si) 50 10]2·6 H20. These amounts of water 

seem high in a fibrous zeolite in which N a is the principal 

cation. In other fibrous zeolites in which N a Is a 

El 
E2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

principal cation-natrolite and mesolite-the ratio of 

H20 molecules to N a ions is 1 : 1, compared to the ratio 

of 3:1 or 2.5:1 for Ca-dominant zeolites like scolecite 

and thomsonite. As N a is the predominant cation in 

gonnardite, H20 would be expected to be lower in 

gonnardite than in thomsonite, rather than the same or 

higher as indicated by these formulas. It is significant 

that in the analyses of gonnardite given by Meixner, 

Hey, and Moss, the two having the highest Na content 

yield molecular ratios for H20 of only 5.14 and 5.19. 

The purpose of this investigation is to study the 

degree and kind of variation in composition that occurs 

in the thomsonites and gonnardites, and the relation of 

these minerals to each other, and to examine the problem of the water content of gonnardite. The analyses 

of thomsonite used were selected from those reported 

or cited by Hey {1932), using only analyses published 

after 1885, in which the sum of the tetrahedral atoms 

was 10.0±0.10. In addition to the analyses of gonnardite published by Meixner, Hey, and Moss, several 

other recent analyses from the literature were also used. 

Atomic ratios were calculated from the analyses on 

the basis of 20 oxygen atoms, and represent, according 

to Hey's {1955, p. 166) formulas, quarter-cell values for 

thomsonites and half-cell values for gonnardites. 

THOMSONITE 

N Rt.oCa2.oAh .oSi.oi .o02o·6.0 H20 

Atomic ratios for selected post-1885 analyses of 

thomsonite reported or cited by Hey {1932) are given in 

tables 1 and 2 together with calculated values for H20. 

The atomic ratios show wide ranges in the values for 

Si and AI. The ranges for Ca and N a are even greater, 

from 2.14 to 1.00 for Ca, from 0.74 to 2.71 for Na, and 

from 2.58 to 3.71 for (Ca+Na). However, Ca values 

greater than 2.00 are found in only four analyses and 

these values are 2.02, 2.04, 2.07, 2.14. Values for Na 

less than 1.00, were found in only seven; of these seven, 

only three, 0.89, 0.88, and 0.74, are less than 0.90. 

Both types of replacement recognized in thomsonite 

affect the Ca and N a content, consequently the kind 

and amount of replacement can be estimated only by 

other deviations in composition. A Si value greater 

than 5.00, the theoretical amount according to the 

above formula for thomsonite, together with an AI value 

deficient by about the same amount, indicates replacement of an equivalent amount of Ca by Na. A positive 

difference in the expression [(Ca+Na)-3.001 indicates 

that this amount of Ca has been replaced by N a2 ; a 

negative result indicates the amount of Ca replacing 

Na2• The fact that in the ranges inCa and Na quoted 

above most Ca values are less than 2.0, with few significantly above, and that most N a values are greater than 

1.00, with few significantly less, indicate( that replaceTABLE 1.-Atomic ratios calculated from analyses of thomsonite 

reported by Hey, 1932 

[Numbers refer to Hey, 1932, table 1, p. 54-55] 

H20 

No. Ca(+Mg) Na(+K) (Ca+Na) AI Si Deter- Calcu- Di1fermined lated ence 

-------- 1 _____ 1. 62 1.48 3.10 4. 52 5.43 6.34 5. 53 +0.81 

2.---- 1.67 1.20 2.87 4. 57 5.42 5. 58 5.38 +.20 a _____ 1.84 . 74 2. 58 4. 58 5.46 6.10 5.34 +-76 4----- 1. 71 .89 2. 60 4. 62 5.46 6.44 5.17 +1.27 5 _____ 1.00 2. 71 3. 71 4. 62 5.36 5.48 5. 21 +-27 

6.---- 1. 41 1. 70 3.11 4.62 5.40 6.44 5. 22 +1.22 

7----- g 1. 72 1.18 2.90 4. 65 5.36 5.50 5.48 +.02 _____ 1. 76 1.24 3. 00 4. 68 5. 29 6.12 5. 64 +.48 

9.---- 1.45 1. 71 3.16 4. 70 5.32 5.46 5.33 +.13 10 ____ 1.82 1. 24 3.06 4. 73 5.23 5. 92 5. 79 +-13 

11. ... 1. 74 1. 26 3.00 4. 78 5. 23 5.89 5. 61 +-28 12 ____ 1. 98 1. 22 3.20 4.87 5. 06 5.82 6.17 -.36 13 ____ 2. 08 .88 2.96 4. 90 5.06 6.10 6. 08 +.02 14 ____ 1. 98 .97 2. 95 4. 93 5. 07 5.61 5. 92 -.31 15 ____ 2.00 1.04 3.04 5.03 4. 97 5.95 6.04 -.09 

16 •••• 2.02 .94 2. 96 6.04 4.98 6.17 5.99 +-18 

TABLE 2.-Atomic ratios calculated from selected post-1870 

analyses of thomsonite cited by Hey, 1932 

[Numbers refer to Hey, 1932, table 2, p. 58-64] 

No. Ca(+Mg) Na(+K) :cca+Na) AI Si Determined 

---- 24a ___ 1. 59 1. 58 3.17 4. 76 5. 24 5.52 29 •••• 1. 56 1.30 2.86 4.64 5.40 5.42 

32 ••.. 1.94 1.04 2.98 4.98 5.04 6.23 33 ____ 1.98 1.10 3.08 5.06 4.94 6.00 45 ____ 1.96 1.04 3.00 5.03 4.98 6.08 

47 ____ 1.92 1.16 3.08 4. 78 5.16 6.03 

49 •..• 2.04 1.01 3.05 5.02 4.91 6.05 54 ____ 1.84 1.10 2.94 4. 80 5.20 5.98 58 ____ 1.94 1.10 3.04 4.95 5. 05 5.81 

64---- 1.94 .91 2.85 4.93 5.11 5. 73 

66 ____ 1.18 2.18 3.36 4. 67 5.37 6.54 69. ___ 1.58 1.62 3.20 4. 72 5. 26 5.08 7L ___ 1.64 1.30 2.94 4. 57 5.43 5.84 72 ____ 1.68 1.06 2. 74 4. 78 5. 22 5.64 

76---- 1. 73 1.06 2. 79 4.83 5. 24 5. 71 

78 ____ 1. 68 1. 21 2.89 4.62 5.40 5. 68 79 ____ 1. 68 1.14 2.82 4.68 5.36 5. 66 go ____ 1.54 1.24 2. 78 4. 50 5. 56 5.34 81. ___ 1.60 1.43 3.03 4. 60 5.39 5. 68-< 

83---- 1. 59 1.36 2. 95 4.60 5.42 5. 77 

92a 94 ____ ... 2.14 .95 3.09 5.02 4.92 6.~ 1.97 1.04 3.01 4.98 5.02 5.90 95 ____ 1. 74 1.05 2. 79 4.96 5.02 5. 79 100 ___ 1.64 1. 50 3.14 4.61 5.36 5.59 

HsO 

Calcu· 

Ia ted 

--

5.56 

5.20 

5. 89 

6.05 

5. 94 

5. 96 

6.11 

5. 70 

5.95 

5. 76 

5.13 

5.57 

5.40 

5. 26 5.38 

5.41 

5.34 

5.09 

5.43 

5.34 

6.30 

5.96 

5.40 

5. 60 

Di1ference 

--

-0.04 

+.22 

+-34 

-.05 

+-.14 

+.07 

-.06 

+-28 

-.14 

-.03 

+1.41 

+.49 

+-44 

+.38 

+.33 

+.27 

+.3 

+.25 2 

+.2 5 

+-43 

-.0 6 

06 

9 

1 

-

+-3 

-.0 

ment of Ca by N a, by one method or the other, greatly 

predominates over the reverse and that replacement of 

Na by Ca is of relatively little importance in the 

thomsonites. 

The atomic ratios yielded by some analyses of thomsonites are so close to the theoretical values that little 

replacement of either type is indicated. For example, 

in No. 15, table 1, none of the atomic ratios deviate 

more than 0.04 from the theoretical values, and the 

molecular value for H20 is 5.95 as compared with 6.00. 

Other analyses whose atomic ratios, given in tables 1 

and 2, are very close to the theoretical values, are Nos. 

14, 16, 32, 33, 45, 49, and 94. The Si, AI, and (Ca+ N a) 

values for all the other analyses whose atomic ratios 

are given in tables 1 and 2 indicate both types of replace-
COMPOSITIONAL RELATIONS AMONG THOMSONITES, GONNARDITES, AND NATROLITES E3 

ment, except for Nos. 8, 11, and 81. In these replacement of CaAl by NaSi is indicated; the (Ca+Na) 

values of 3.00 and 3.03 indicating that no N a2~Ca 

replacement has occurred. 

In almost all the analyses in which both types of 

replacement are indicated, the Si value is usually 

greater than 5.00 and the AI value is less, indicating 

that replacement of CaAl by NaSi is more common in 

thomsonites than replacement of NaSi by CaAl. 

With respect to Na ~Ca replacement, 17 of the 40 

(Ca+ N a) values in tables 1 and 2 are greater than 3.00, 

indicatng replacement of Ca by N a2, and 20 are less 

than 3.00, indicating replacement of N a2 by Ca. As in 

most thomsonites replacements of the N aSi~CaAl 

type are of NaSi for CaAl. Thus in some there is dual 

replacement by Na, but in others there is both replacement of CaAl by NaSi and replacement of Na2 by Ca, 

with the replacements offsetting each other to greater 

or less degree. Although the thomsonites whose atomic 

ratios are given in tables 1 and 2 differ widely in content 

of Ca and N a, the sum of the atomic ratios for Ca and 

Na, (Ca+Na) is quite constant, 3.00±0.20 in all but 

eight of the analyses (Nos. 3, 4, 5, 66, 72, 76, 80, and 

95). In Nos. 76 and 80 the difference is only 0.21 and 

0.22, respectively. 

The relation between~ Ca and N a in thomsonites is 

shown graphically in figure 1. The points representing 

thomsonites whose atomic ratios for Ca and N a are 

close to the theoretical 2.00 and 1.00, respectively, 

cluster closely around the asterisk that represents 

theoretical thomsonite. A few points fall a very short 

way along the line representing N ~Ca replacement, 

but more fall along or below the line representing NaSi 

replacement of CaAl. However, none fall as far along 

this line as the asterisk representing theoretical faroelite. 

Even the point representing the average Ca and Na 

ratios for the five Faroe Islands zeolites cited by Hey 

(1932)-Nos. 19, 21, 22, 23, and 24a-fall short of this 

point. Farther out along this line is the point 

representing the "gonnardite" calculated by Hey 

(1932) from an analysis of a spherulite made up of 

thomsonite and gonnardite. The points that fall 

below the NaSi~CaAl replacement line represent 

thomsonites in which replacement of CaAl by NaSi 

is accompanied by some replacmnent of Na2 by Ca. 

Most of the points representing the Table Mountain, 

Colo., thomsonites (Nos. 78, 79, 80, 81, and 83, table 

2), fall in this area. 

The points representing the relation between Ca and 

Na in thomsonites that have the highest Na content 

(Nos. 5, 9, 24a, 66, and 69) fall along a line between 

the N -~Ca replacement and the N aSi-~CaAl 

replacement lines. This middle line represents dual 

replacement: replacement of Ca by Na2 and of Ca as 

4.0 1\ ' ' \ 

\ 

\ 

3.6 '~ 

3.2 

2-8 

0 2.4 

~ 0:: 

(..) 

~ 2.0 

0 

~ ro 

Z L6 

1.2 

o_s 

0. 4 

\ f' ,>,. 

\ l'~~ '8 '" ~ \~ ~&· J \~ G\1. ~- ,'?-

'~ "' ~ C"(i) ' "...., ~ \ 

"~,{. ~ \ ~c ,... \ 

'{-?. \ \ i ~ ' '\-, 66. 1\\ - I I ' 0 (1\0 Hey's gonnardite '- 0~ 

Wincrell's end1 member ~,~~G 

J The~retical fa,roelite~x. D (Ill) Hey's high-Si thomsonite/ 

; 

Average fa roe lite 

\ 

\ 

t4a 

~' ·:~ ~l Theoretical 

4\ ~omsonite 

• • 

• ·~ \" ', \ 

\ 

' 

\~, 

0 0.4 0.8 L2 1.6 2.0 2.4 2.8 

Ca ATOMIC RATIO 

FIGURE 1.-Relation between Ca and Na in thomsonites. 

CaAl by NaSi to the same degree. The highest N a 

ratio in tables 1 and 2 is that in analysis 5, but the 

highest Na ratio in the analyses cited by Hey (1932) 

is in analysis 28. The value he gives, 12.50, is for the 

unit cell, which would be 3.125 in terms of the quarter 

cell as used in this study. In the same terms the ratio 

for Ca is only 0.68. The point representing the relation 

between Ca and N a in this analysis falls considerably 

farther along the dual replacement line than does the 

point representing No. 5 which actually falls between 

the dual replacement line and the Na -~Ca line. 

Analysis 28 is cited by Hey as that of a thomsonite. 

although it had been earlier considered to be that of 

a mesolite. It was not included in table 2 because of 

its age (1836). 

The relation between Ca and H20 in thomsonites is 

shown graphically in figure 2. Although thomsonites 

that have the same Ca ratio may differ greatly in H20 

content, the points in figure 2 do show a general downward trend in H20 content with decrease in Ca. In 

general, analyses having high Ca contents tend to have 

high H20 contents, and analyses having low Ca contents tend to have low H20 contents, except for analyses 

1, 4, 6, and 66, in which H20 is very high. The points 

representing these analyses fall completely outside the 

pattern made by the other points. 
E4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

6.60 

6.40 

6.20 

0 

~ 6.00 a::: 

a::: 

<( 

.....J a 5.80 LLI 

.....J 

0 

:2: 

q, 5.60 

:c 

5.40 

5.20 

r5.00 

0.80 

66. 

~6(H) 4(H)x 

xl(H) 

• /. 

EXPLANATION (H)x x(Hi ~(~(H) x<H) • 

Analyses reported by Hey 

*:(Hh \ • (H)x ) . Analyses cited by Hey • I (~)X 

~I Theoretical 

• tt omsonite 

x(H) 

x<;/. 

v·x(H) 

5(H) (H)x 

I/. 

• 

1.00 1.20 1.40 1.60 1.80 2.00 2.20 

Ca ATOMIC RATIO 

FIGURE 2.-Relation between Ca and H20 in thomsonites. 

GONNARDITE 

Na2.oCa1.0Al4.0Si6.002o·7 H20 

Five analyses of gonnardite were published by 

Meixner, Hey, and Moss (1956), including two (D and 

E) that Hey had published in 1932 as an analyses of 

gonnardite-thomsonite spherules. The outer part of 

the spherules was described as thomsonite, and the inner 

part as gonnardite. When the analyses were republished as analyses of gonnardite, no explanation was 

given as to why analyses originally published as analyses 

of a composite sample were republished 24 years later 

as analyses of a single mineral. In 1932 Hey had 

prorated the constituents found in these analyses between a high-silica thomsonite and hypothetical 

gonnardite on the basis of assumed compositions and 

of the proportion of each estimated to be present in the 

spherule analyzed. The half-cell atomic ratios for this 

calculated gonnardite, D(IV), are given in table 3. 

Also given in table 3 with their atomic ratios, are 

analyses A, B, C, and D of Meixner, Hey, and Moss 

(1956), two other analyses of gonnardite from the 

literature, and three recent analyses of high-N a 

mesolite. The Bulgarian material (Kostov, 1958) 

analyzed was called "gonnardite (with thomsonite?)." 

The analysis of the material from Norway is an old one 

by Paijkull (1874). This material was originally 

called ranite, but Mason (1957) recently identified it as 

gonnardite. The analyses of high-N a mesolites given 

in the last three columns of table 3 indicate compositions 

very similar to that of gonnardite or high N a thomsonite. 

The relation between the atomic ratios of Ca and N a 

given in table 2 is shown graphically in figure 3. Also 

shown in figure 3 is the relation between Ca and N a in 

TABLE 3.-Analyses of gonnardites and high-Na mesolites, and their atomic ratios 

[In order of increasing Na20 content} 

Si 02-------------------------------------------------------------- AhOs------------------------------------------------------------- CaO ----------_ ---------_- _ --------- _ --_ --_________ --- ___________ _ 

K20 N a20 ___ -----_ ------------------------------------------------------- ---_______________________________________________________ _ 

H20-------------------------------------------------------------- Total ____ ---------------------------------------------------

SL- _ ------------------------------------------- __ --------------- _ AL ____ --------------·-------------------------------------------- (Ca+ Mg) _ ----__________________________________________________ _ 

(N a+ K) ____ ----------- _____ ------------------------------------ _ 

~~~;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:~~~~ 

D D(IV) I c 

Composition (percent) 

41.85 ---------- 27. 02 ---------- 9.29 ---------- 7.25 

n.d. ---------- 14.37 ---------- 99.78 ----------

42.75 

27.36 

7. 77 8.15 

.15 

13.44 

99.62 

Gonnardites 

2 

42.71 39.21 30.16 31.79 6.25 5.07 9. 50 11.55 

---------- ---------- 111.70 11.71 3100.50 4 99.90 

Atoms per halt cell (20 oxygens) 

5.64 5.8 5.69 5.52 5.18 

4.29 4.2 4.29 4.59 4.95 

1.34 1.0 1.11 3.90 .72 1.89 2.0 2.12 2.37 2.96 

3.23 3.0 3.23 3.27 3.68 

6.46 5.97 4.85 5.16 

5.91 ---------- 5.45 5.07 5.12 

+.55 ---------- +.54 -.22 +.04 

4 Includes 0.57 Fe20a. 

High-Na mesolites 

A B 3 4 5 

42.80 43.20 40.03 41.15 40.59 28.15 27.90 27.88 29.49 29.69 4.26 3.61 6.03 5.33 5.06 12.65 13.16 10.05 11.02 11.00 .13 Trace .40 .25 .51 11.85 11.74 2 11.10 13.52 13.58 99.84 99.61 1100.29 100.76 100.43 

5.62 5.67 5.48 5.45 5.41 4.36 4.32 4.50 4.60 4.66 .60 .51 .92 • 76 • 72 3.24 3.35 2. 73 2.86 2.92 3.84 3.86 5 3.65 3.62 3.64 5.19 5.14 5.07 5.97 6.03 5.04 4.88 5.49 5.14 5.08 +.15 +.26 -.42 +.83 +.95 

1 Includes 0.45 H20-. 2 Includes 3.12 HsO-. a Includes 0.18 MgO (0.04 Mg atomic ratio). 

!Includes 0.85 Fe20a, 0.59 FeO, 0.22 MgO (0.04 Mg atomic ratio) and 0.02 Ti01. 

LOCALITY AND REFERENCE 

D. Chaux de Bergonne, France, Mei,xner, Hey, and Moss, 1956, p. 266. D(IV). Hypothetical composition of gonnardite, calculated by Hey (1932, p. 117) 

from D. 

C. Aci Castello, Sicily, Meimer, Hey, and Moss, 1956, p. 266. 1. Bourgas Spa, Bulgaria, Kostov, 1958, p. 16, no. 1. 2. Langesundsfjord, Uven, Norway, Dana, 1892, p. 609 (ranite). 

FOR ANALYSES IN TABLE 7 

A. Klock, Styria, Meimer, Hey, and Moss, 1956, p. 266. B. Aci Trezza, Sicily, Maimer, Hey, and Moss, 1956, p. 266. 3. Rio Cambone, Montiferro, Sardinia, Deriu, 1954, p. 42. 4, 5. Kladno, Bohemia, Antonin, 1942, p. 11. 
0 

t= 

<( 

a:: 

u 

~ 0 

1-

<( 

co 

z 

COMPOSITIONAL RELATIONS AMONG THOMSONITES, GONNARDITES, AND NATROLITES 

40*~~--~-,--~------.----------,r----------r----------r---------~--------~ 

· ·~Theoretical \ natrolite \ 

\ 

0 \ 

\ 

\ 3.6 0 \ 

\ 

Upper limit of\ 

EXPLANATION 

X 

• 8 " \ Gonnardites R

/ gonnardite \ 

\ 

3.2t------+-____)~\xo..:...A:...__...,....Jor-w-a~~\-~----1---------l 

<~ 

"' ,CJ ' \~ ' ~ 2.8 t-----~~'%-J)-~+-~--:'l.----.\..--1\-----\\\ 

• 

High-Na thomsonites 

High-Na mesolites 

0 

Natrolites 

~~ ~ :Or.: \ 

4r---------~----~~.~~ X ~~~~'r,-,------+---------~~---------+----------~ 

~' ~~·1\ ', or---------~-----------r-----'·~*~----+1--~~r---'~~----------4-----------~--------~ 

2. 

2. 

" Dx ' 

Winchell's end member'6 \ 

Hey's gonnardi~ ~ 

I ' 6• e9 \Lower limit of 

" 69 • ~-\ gonnardite L6r---------~-----------r----------4-----~~~~~-------4----------~--------~ 

Hey ~he~re!ica! s h1gh-S1 thomsonite 

faroelit~~· o. ~ Average faroelite 

\ 

\ 

"'\,. ~~ Theoretical 

'jthomsonite 

~" 0.8 r---------t-----t----+-----"'-----1-----t----\~~~.~~~--""----l--""--1 

OAr---------~-----------r----------4-----------~---------4--------~~----~--~ \\ "' '\" \ '\, 

\ 

\ 

0~------~~------~------~~------~~------~~-------L-~'--~~ 0.4 0.8 1.2 1.6· 2.0 2.4 2.8 

Ca ATOMIC RATIO 

FIGURE 3.-Relation between Ca and Na in gonnardites, and high-Na thomsonites and mesolites. 

E5 
E6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

the high-N a thomsonites given in tables 5 and 6, 

Nos. 1, 5, 6, 9, 24a, and 66. The relation between Ca 

and Na in No. 28, which had the highest Na content of 

the thomsonites cited by Hey (1932), is also shown in 

figure 4. The material represented by this analysis had 

previously been called mesolite. The points representing gonnardites intermingle with points representing 

high-N a thomsonites and mesolites, and all the points 

fall close to and along the line representing dual replacement, in equal amounts, of Ca by Na2 and Ca as CaAl 

by NaSi. On the other hand, the point representing the 

relation between Ca and N a in the gonnardi te D (IV), 

calculated by Hey from analysis D falls on the line 

representing NaSi---:)CaAl replacement at a point 

equivalent to 50 percent replacement of the Ca in 

thomsonite as CaAl, and a step beyond the point representing theoretical faroelite, which is equivalent to a 

replacement of 25 percent of the Ca in thomsonite as 

CaAl. The point representing the thomsonite calculated by Hey, D (III), also falls on the N aSi---:)CaAl 

replacement line a little below the point representing 

theoretical faroelite. Thus the points for "gonnardite" and "thomsonite" calculated by Hey from 

analysis D both fall on the NaSi---:)CaAl replacement 

line, whereas the point representing D itself falls much 

closer to the line representing dual replacement. 

The intermingling of points representing the relation 

between Ca and N a in gonnardites, high-N a thomsonites, and so-called mesolites along the line representing 

dual replacement of Cain thomsonite suggest that all 

these zeolites may belong to an isomorphous series 

characterized by dual N aSi---:)CaAl and N a2---:)Ca 

replacement, and that theoretical thomsonite, 

Ca2. Na~.~ .oSi .o02o·6.0 H20, is the high Ca end 

member of this series. 

A THOMSONITE-GONNARDITE-NATROLITE 

ISOMORPHOUS SERIES? 

Gonnardites and high-N a thomsonites can both be 

interpreted as derived from normal thomsonsite by dual 

replacement, to about the same degree of Ca by N a2, 

and of CaAl by NaSi. Steps in this dual replacement, 

starting with thomsonite, are shown in these formulas. 

Thomsonite: N at.oCa2.oAls.oSis.o02o · 6.0 H20 

N a us Ca1.5oAl4.7sSis.2s02o · 5.5? H20 

N a2.soCa1.0oAluoS:ia.so02o · 5.0? H20 

Naa.2sCao.ooAk2s Si5.7s02o·4.5? H20 

N atrolite: N a4.0oCao.ooAl4.0oSi6.oo02o · 4.0 H 20 

The atomic ratios for No. 9, table I, are very similar 

to those in the second formula, which represents the 

first step in the replacement. The atomic ratios for 

the analyses of gonnardite from Bulgaria and the highN a mesolite from Sardinia, table 3, are similar to those 

in the third formula, and the atomic ratios for analysis 

A and B, table 3, are similar to those in the fourth 

formula. The Ca-free end member is identical with 

the formula for natrolite. Points representing the 

relation between Ca and N a in several natrolite analyses, 

Nos. 12, 15, 17, 22, and 25 (table 1), fall on or close to 

the upper end of the line representing dual replacement 

in figure 3. The gonnardite (B, table 3) having the 

highest Na content has a Na atomic ratio only 0.26 

below the N a atomic ratio in the natrolite having the 

highest Ca content (No. 25, table 1). The formulas 

for these two analyses are: 

Analysis B, table 3: Naa.ssCa.stA4.a2S4.6702o·5.14 H20 

Analysis 25, table 1: Naa.61 Ca.27AlusS4.7702o · 4.37 H20 

The sum of the cations (Ca+Na) also agrees closely, 

3.86 and 3.88 in B and No. 25, respectively. 

The high-Na mesolites given in table 3 may be 

interpreted as either derived from thomsonite by 

replacement of 0.40-0.50 CaAl by 0.40-0.50 NaSi, 

plus replacement of 0.60-0.65 Ca by 1.20-1.30 N a2, or 

as derived from mesolite by replacement of about 

0.50 CaSi by an equivalent amount of N a3Al. 

Deer, Howie, and Zussman (1963, p. 358-359) give 

.the following ranges in indices of refraction for thomsonite, gonnardite, natrolite, and mesolite: 

Optic 

axial 

sign a fJ 

Thomsonite______________________ + 1. 497-1.530 1. 513-1.533 1. 518-1.544 

Gonnardite __ -------------------- 1. 497-1.506 -------------- 1. 499-1.508 Natrolite_________________________ + 1. 473-1.483 1. 476-1.486 1. 485-1.496 

M::--fo~::--~::: ~ a:::::~-- o~·:t ~g:~:: thomsonites whose analyses are given in tables 1 and 

2 and on the gonnardites and the high-Na mesolites 

whose analyses are given in table 3; 

Source 

High-Na thomsonites 

!_________________ 1. 511 

5_________________ 1. 523 6_________________ 1. 518 g_________________ 1. 517 

1. 513 1. 518 Hey, 1932, p. 54. 1. 525 1. 527 Do. 1. 520 1. 528 Do. 1. 519 1. 526 Do. 24a_______________ 1. 521 1. 523 1. 528 Hey, 1932, p. 80. 

Gonnardites and high-Na mesolites 

A 1_______________ 1. 498 1. 502 B 1_______________ 1. 497 1. 499 c 1 _______________ 1. 506 1. 508 D 1______________ 1. 506 1. 508 

Norway 1________ 1. 513 1. 515 Sardinia _________ 1.5044 1.5052 1.5067 

Meixner, Hey, and Moss, 1956, p. 266. Do. 

Do. 

Do. Mason, 1956. Deriu, 1954. 

1 The indices of refraction given are not true a and true 'Y• but a' and 'Y'· 
COMPOSITIONAL RELATIONS AMONG THOMSONITES, GONNARDITES, AND NATROLITES E7 

z 

0 

1.536 

1.532 

~ 1.528 <( 

0:: 

LL.. 

IJJ 

0:: 

~ 1.524 

X 

IJJ 

0 

~ 

z 1.520 <( 

IJJ 

:E 

1.516 

X 

1.512 

18.0 

X 

X XX 

18.4 

X X 

X 

X 

X 

X X 

X 

X X 

18.8 19.2 19.6 20.0 20.4 

AI ATOMS PER UNIT CELL 

FIGURE 4. Relation between AI atoms per unit cell and mean 

index of refraction in thomsonites. 

Hey (1932) found that the indices of refraction of 

thomsonite increase with increase in .A.l, but are little 

affected by replacement of Ca by N a2, or vice versa. 

The relation between AI atoms and Na atoms per unit 

cell and the mean index of refraction in 16 thomsonites 

whose analyses were reported by Hey (1932) are shown 

in figures 4 and 5. The general trend of the points 

in figure 4 is upward with increase in .A.l content and 

mean index of refraction, but the relation is not precise, 

as some thomsonites having the same AI content may 

differ considerably in mean index of refraction and 

vice versa: The location of the points in figure 5 

indicates little relation between Na content and mean 

index of refraction. For example, six thomsonites 

having about the same number of N a atoms per unit 

cell, 4.74 to 5.04, range in mean index of refraction 

from 1.521 to 1.535. Thus the wide ranges in the 

indices of refraction of thomsonite seem to reflect the 

wide range in AI content, or conversely, Si content, 

in thomsonites, rather than variations in N a content 

orCa content. 

Gonnardites are characterized by varying NaSi --7 

Ca.A.l and N a2-7Ca replacement, and should vary considerably in AI content, and, presuming the same 

relation as in thomsonite, in indices of refraction. 

The ranges in the indices of refraction for gonnardite 

given by Deer, Howie, and Zussman are coextensive 

with the ranges for prime (') indices of refraction of 

gonnardite reported by Meixner, Hey, and Moss (1956), 

and are presumably based on them. Thus the ranges 

given by Deer, Howie, and Zussman for the indices of 

1.536 

1.532 

z 

~ 1.528 

(.) 

<( 

0:: 

LL.. 

IJJ 

0:: 

~ 1.524 

X 

IJJ 

0 

~ 

z 

~ 1.520 

~ 

1.516 

1.512 

2.0 

• 

• 

• • 

• 

• 

• 

• 

• 

• • • 

• • 

' 

4.0 6.0 8.0 10.0 12.0 

Na ATOMS PER UNIT CELL 

FIGURE 5. Relation between Na atoms per unit cell and mean 

index of refraction in thomsonites. 

refraction of gonnardite are based on four sets of a' 

and 'Y' values. .Although these four gonnardites vary 

widely in N a content, from 1.89 to 3.35 atoms per 

half cell, they are very similar in AI content, varying 

only between 4.29 and 4.36 atoms. This is because in 

D and 0, which have the lower N a contents, 1.89 

and 2.12 atoms per half cell, replacement of Ca.A.l by 

NaSi is greater than replacement of Ca by Na2, whereas 

in A and B, which have the higher N a contents, 3.24 

and 3.35 atoms per half cell, replacement of Ca by Na2 

is greater than replacement of Ca.A.l by NaSi. In all 

four the amount of NaSi replacement of Ca.A.l is about 

the same, 0.62+0.70 Ca.A.l replaced by equivalent 

amounts of NaSi, but the amount of Ca replaced by 

N a2 varies from 0.23 in D and 0, to 0.84 in A and 0.86 

in B. Consequently all four have about the same 

.A.l content and about the same indices of refraction. 

The relative degree of NaSi or Na2 replacement is 

indicated by where the points representing these gonnardites fall with respect to the dual replacement line 

in figure 3. 

The prime (') indices of refraction reported by Mason 

(1957) for the Norwegian zeolite that he identified as 

gonnardite are somewhat higher than those reported 

for analyses A, B, 0, and D, as its higher AI content 

would suggest, 4.95 atoms per half cell. The indices 

of refraction reported by Hey for the high-N a thomsonites whose points intermingle with those of gon-
ES SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

nardite along the dual·replacement line in figure 3 

are also higher than those for gonnardites A, B, C, and 

D. The high-Na thomsonites are also higher in AI 

content than these gonnardites, having relatively 

less replacement of CaAl by NaSi-from 0.24 to 0.46, 

compared to 0.62 to 0.70 in A, B, C, and D. The 

indices of refraction for these high-N a thomsonites 

fall within the ranges of indices for thomsonites. 

It is probable that further data on the indices of 

refraction of gonnardite will extend the ranges of the 

indices of refraction of this zeolite and may show that 

the ranges of the indices of refraction for gonnardite 

overlap to some extent those for thomsonite. 

The ranges for the indices of refraction of natrolite 

and mesolite are very narrow, just as their variations 

in AI content are very small. 

The structural similarities between thomsonite, 

gonnardite, and natrolite are well known. All three 

zeolites have framework structures in which every 

(Si, Al)04 tetrahedron has each of its oxygens shared 

with another tetrahedron; linkages to form chains in 

the z direction are the most prominent. The repeat 

unit in each chain consists of five tetrahedra and occupies about 6.6A. However, natrolite and thomsonite 

differ considerably in detail. The structures of thomsonite and natrolite are described by Deer, Howie, and 

Zussman (1963, p. 361-362) "In thomsonite neighboring chains in they direction are related by mirror planes 

(010), but those in the x direction are related by diad 

axes [010]. The resulting unit cell (orthorhombic 

Pnma) contains four chains * * * . In the structure 

of natrolite, neighboring chains are related (approximately) by diads only, and this results in a bodycentered cell with dimensions similar to those of 

thomsonite (a::::::b::::::13.1A) or a face-centered cell with 

a 18.3, b 18.6A * * * . The difference between AI 

and Si tetrahedra and perhaps other deviations from 

the ideal structure result in orthorhombic (pseudotetragonal) cells for both thomsonite and natrolite. 

In thomsonite, moreover, such deviations give rise also 

to a double c parameter (13.25::::::2X6.63)." The 

structure of gonnardite is described by Deer, Howie, and 

Zussman (1963, p. 364) as follows, "Gonnardite has 

cell parameters similar to those of thomsonite and is 

assumed to have a similar aluminosilicate framework 

structure. X-ray fibre photographs of gonnardite are 

similar to those of thomsonite, and its powder photographs may be confused with those of natrolite (Meixner 

et al., 1956)." Natrolite is the only one of these three 

zeolites whose structure has been refined (Meier, 1960). 

As the structures of these minerals are similar but 

differ in detail, it may be that, although analyses suggest a continuous series compositionally, there is a 

structural change somewhere between thomsonite and 

natrolite. Such a change would be analogous to the 

structural change from dioctahedral to trioctahedral 

which occurs halfway between muscovite and lepidolite, 

and which breaks the continuity of the compositional 

series consisting of muscovite, lithian muscovite, and 

lepidolite (Foster, 1960). 

Hey (1932) concluded that the optical properties and 

X-ray spacings of gonnardite furnish fairly conclusive 

evidence that it should be regarded as a separate species 

related to thomsonite perhaps in a manner like that of 

a- and 13-quartz. He tentatively identified gonnardite 

with metathomsonite, a high-temperature polymorph 

of thomsonite. The transition from thomsonite to 

metathomsonite is reversible and the transition temperature is dependent on the water content. The two 

forms are compositionally the same, except for water 

content. On the other hand, gonnardite differs in 

composition from thomsonite, being intermediate in 

composition between thomsonite and natrolite, and 

cannot become thomsonite simply by a decrease in 

temperature and rehydration as metathomsonite does. 

To obtain thomsonite from gonnardite requires chemical 

change. 

Hey (1955, p. 166) gives the H20 content of gonnardite as 7 molecules per 20 oxygen atoms. The next 

year Meixner, Hey, and Moss (1956) give the H20 

content as 6 molecules per 20 oxygen atoms. It has 

been noted that in natrolite and mesolite the ratio of 

H20 molecules to Na ions is 1:1, and that in scolecite 

and mesolite the ratio of H20 molecules to Ca ions is 

3: 1. In thomsonite the ratio of H20 molecules to N a 

ions is again 1:1, but the average ratio of H20 molecules 

to Ca ions is 2.5: 1. Analogously, it would be expected 

that gonnardites would contain less water ~han thomsonites, because of the higher Na content and lower Ca 

content. Also, as they are intermediate in chemical 

composition between thomsonite and natrolite, they 

would also be expected to be intermediate in H20 

content. In the analyses of gonnardite given by 

Meixner, Hey, and Moss, the water content per 20 

oxygen atoms varies from 5.35 to 6.1, molecules. In the 

analyses given in table 3, which includes four of the 

analyses of Meixner, Hey, and Moss, H20 varies from 

4.85 to 6.46, and averages 5.54 molecules. The average 

molecular ratio for H20 in the high-N a thomsonites that 

fall close to or on the middle line (Nos. 5, 9, 24a, 66, 

and 69) is 5.42. The average molecular ratio for H20 

in all the analyses whose Ca: N a ratio falls on or close to 

the dual replacement line in figure 3 is 5.50. For 10 

of these 15 analyses the molecular ratio for H20 is less 

than 5.50, in three it is close to 6.00, and in two it is 

more than 6.40. Such H20 values tend to support the 

hypothesis that in zeolites that are intermediate in 

composition between thomsonite and natrolite the 
COMPOSITIONAL RELATIONS AMONG THOMSONITES, GONNARDITES, AND NATROLITES E9 

content of H20 should also be intermediate, and that 

H20 contents of 6.00 or 7.00, as assumed in formulas for 

gonnardites, are too high. In this connection it 

should be taken in to consideration that the average 

given above is based on total H20, as only two of the 

analyses upon which this average is based reported 

H20-. Therefore the true H20 content of these 

zeolites is probably somewhat lower than this average. 

FORMULATION 

The formula given by Hey (1955) for gonnardite, 2 

[Na2CaAI4Sis020 ·7H20], can be derived from thomsonite only by unilateral replacement of CaAI by NaSi, 

as illustrated below: 

Thomsonite: N al.OCa3.oAio.oS:is.o02o·6.0 H20 

Faroelite: N au Ca1.5AluSio.o020·6.0 H 20 

Hey's gonnardite: Na2.oCa1.oM.oSi6.0020·7.0 H20 

However, the atomic ratios of all the analyzed gonnardites, as well as the atomic ratios of most of the 

high N a-thomsonites, indicate dual replacement; replacement of CaAI by NaSi, and replacement of Ca by 

N a2 to about the same degree. Therefore, the formula 

given by Hey for gonnardite does not reflect the composition of gonnardite as indicated by analyses, nor 

does it reflect the great variation in composition found 

in the materials that have been called gonnardites. 

Nor does the formula usually given for thomsonite reflect the range in composition found in the thomsonites. 

The usual thomsonite formula is that of the end member, which bears the same relation to thomsonites in 

general as phlogopite bears to phlogopites in general, 

and which bears the same relation to gonnardite that 

phlogopite bears to biotites. 

It is obvious that members of a replacement series 

that vary in composition and that merge into one another cannot be adequately characterized by formulas 

that indicate fixed relations between the constituents. 

For members of such a series only formulas that indicate permissible limits of composition are adequate. 

The limits of composition with respect to Na and Ca 

between thomsonite and gonnardite and between gonnardite and natrolite suggested herein are selected 

arbitrarily because the analyses indicate considerable 

continuity, with no natural breaks along the line joining 

thomsonite and natrolite (fig. 3). The suggested 

upper limit for thomsonite is at a dual replacement of 

0.20 Ca+0.20 AI by 0.20 Na+0.20 Si and of 0.20 Ca by 

0.40 N a. Starting with theoretical thomsonite, N a and 

Ca at this degree of dual replacement are both 1.60. Up 

to this degree of dual replacement Ca is greater than 

N a, beyond it N a is greater than Ca. At this degree of 

replacement of CaAl by NaSi the Al content is 4.80 and 

the Si content is 5.20. The upper limit of composition 

for thomsonite along the line of dual replacement would 

be, therefore,N a1.soCa1. ooA14 .soSis .2o02o ·5. 60H20. This composition also represents the lower limit of gonnardite. 

The suggested upper limit of gonnardite is at a dual replacement of 0.80 Ca+0.80 AI by 0.80 Na+0.80 Si and 

of 0.80 Ca by 1.60 N a. This degree of replacement of 

CaAI by NaSi results in an AI value of 4.20 and a Si 

value of 5.80. The upper limit of composition for gonnardite would be N a3 .4oCa.4oA14,2oSis.so02o·4.40. H20. 

The complete formulas with these suggested limits 

of composition for thomsonite, gonnardite, and natrolite 

would then be 

Thomsonite: N al.o-1.6Ca2.o-I.&Als.o-4.sSis.o-o.2002o·6.Q-5.6 H20 

Gonnardite: N al.6-a.4Ca1.6-o.4A4.s-uS:is.z-5 .s020·5.6-4.4 H 20 

Natrolite: Naa.4-4.oCao.H.oA4.z-4.0Sis.s-&.o02o·4.4-4.0 H20 

These limits for thomsonite, gonnardite, and natrolite 

are marked in figure 3. In these formulas the values 

for H20 are calculated on the basis of a 1: 1 ratio of H20 

to N a and of 2.5: 1 ratio of H20 to Ca, as in thomsonite. 

In accordance with these range formulas, analysis 

No. 24a, table 2, with 1.58 N a and 1.59 Ca comes just 

within the upper limits for thomsonite, and in 69, table 

2, Ca is just within the lower limits for gonnardite. 

No.1, table 1, falls well within the limits for thomsonite. 

No. 9, table 1, and Nos. 28 and 66, table 2, and all the 

analyses given in table 3 fall within the gonnardite 

range. 

It must be understood that the range formula given 

above for thomsonite applies only to thomsonites 

belonging to this dual replacement series. Thomsonite 

in the NaSi--?CaAiline of replacement would have a 

range formula reflecting the atomic relations in this 

line of replacement, such as 

Ca2.0-l.sNal.o-l.sAis.o-4.sSis.o-s.s02o·6.0-5.25 H20, 

which embraces faroelite. 

OTHER LINES OF REPLACEMENT 

In addition to the two lines of replacement that have 

been discussed, four other possible lines of replacement 

are indicated in figure 3. One of these, like the two 

that have been discussed, is a Ca replacement line, 

replacement of Ca by Na2. The other three are all 

N a replacement lines, continuations of the three Ca 

replacement lines. However, except for a few points 

that fall close to theoretical thomsonite, none of the 

points representing the Ca/N a relations of analyses 

whose atomic ratios are given in tables 1 and 2 fall 

along these lines. Replacement of Na by Ca. in 

thomsonites appears to be quite subordinate to replacement of Ca by N a, and replacement of Ca by N a2 seems 

to be found most commonly in conjunction with 

replacement of Ca as CaAl by NaSi, as along the dual 

replacement line. 
ElO SHORTE.R CONTRIBUTIONS TO GENERAL GEOLOGY 

CONCLUSION 

This study has shown that gonnardites, and several 

high-N a mesolites, and certain thomsonites that are 

characterized by dual N aSi--7CaAl and N a2--7Ca 

replacements, are all intermediate in composition between thomsonite and natrolite, and suggest an isomorphous series between them. However, differences in 

optical properties and in structure cast doubt on such 

an interpretation. Whether all these zeolites are 

members of an isomorphous series between thomsonite 

and natrolite or whether only the high-Na thomsonites 

belong to such a series, and the gonnardites and high-Na 

mesolites are polymorphic forms, are problems that 

require more data, especially on their structures, and 

more study for their clarification. 

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0