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Volume 72, 1942-43
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– 181 –

Descriptions of Zeolite, Titanaugite and Apatite in an Olivine Theralite at Lake Waihola.

By C. O. Hutton.

The zeolite separated from theralite 5698 described above is apparently homogeneous. The specific gravity at 19° C. is 2·25–2·26, and the refractive indices repeatedly determined using a variety of oils to avoid any effects of base exchange, give consistently the values α=1·5073, β=1·5095, γ=1·5160 (each ±0·0003) with γ–α 0·0087. These show that the mineral is not natrolite, but is more nearly allied to the thomsonite group. The optic plane and acute positive bisectrix are parallel to the length of the fibre in nearly all cases in material mounted in Canada balsam. Rarely, however, the fibres are twinned, one segment being positively elongated, the other negatively. This also holds true when the mineral has been mounted in oil, after being warmed on the hot plate just sufficiently to permit mounting in Canada balsam. But if the mineral be mounted in oil without this brief heating, nearly all the fibres are negatively elongated, and but few positively. The same is true of the heated mineral which has been subsequently cooled and mounted in a drop of water. It would seem as if the heating brought about sufficient dehydration to change the optical properties significantly, but the original condition is regained when water is returned into the crystalline mesh. The optical orientation makes it difficult to measure accurately the value of 2V. That calculated from the above refractive indices is about 50°(+), that measured by Dr. Turner on the heated mineral mounted in balsam is generally nearer 60° ± 5°(+) but rarely 30°(+). The composition of the zeolite as determined by Mr. F. T. Seelye is peculiar in its content of K2O, which is abnormally high for a member of the thomsonite group of zeolites.

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Table III—Analysis of Zeolite.
Waihola Zeolite. Mol. Prop. Atomic ratio 80 atoms of 0 in unit cell. Hey's Thomsonite No. 1.
SiO2 42.10 0.701 22.91 40.3
Al2O3 26.87 0.263 17.19 28.5
Fe2O3 0.21
FeO 0.36
MgO 0.35
CaO 5.16 0.092 3.00 11.2
Na2O 8.50 0.137 8.95 5.7
K2O 2.63 0.028 1.83 nil
H2O+ 11.35
H2O− 2.57 0.773 25.26 14.1*
CO2 nt. fd.
TiO2 0.03
P2O5 0.01
MnO 0.03
BaO nt. fd.
SrO 0.04
Cl nt. fd.
100.21 99.9

[Footnote] * Assuming Hey is using total Water.

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After considerable search it has not been possible to find an analysis completely comparable with that of the Waihola zeolite. The nearest approach is one listed by Hey (1932, p. 54, table 1) which is given above. It would appear from this that the Waihola zeolite is a potash-bearing member of the thomsonite group near its extreme end containing thomsonite rich in SiO2 and poor in Al2O3. The refractive indices of the Waihola material are also in accord with the generally decreasing value of the indices towards this end of the group. Further, its analysis, recalculated on the basis of 80 atoms of oxygen per unit cell, would tend to confirm its position in that group, though K2O is more abundant in it than in any thomsonite described by Hey. Its formula would appear to be Ca3Na8.95K1.83 Al17.19S22.91O80 25·26 H2O with Al+Si=40·10 and Ca+Na+K = 13·78. These figures agree fairly well with Hey's data, and the latter would seem to show that the Na⇌K⇌Ca substitution is of importance.

No name is suggested here for this zeolite. Certainly Hey's (1933) work on ashcroftine leaves the term kalithomsonite available, but it seems undesirable to revive it by its application to the Waihola zeolite.

The titanaugite (separated from the thin greenish mantle enriched in aegirine-augite) has the following properties:—Sp. gr. at 16° C. = 3.425±0·005. Refractive indices α = 1·698, β = 1·704, γ = 1·724 (each ±0·001) and γ–α = 0·026. The value of 2V calculated from these figures is about 60°(+), that measured by Dr. Turner on the purplish augites in this rock varies from 48°(+) to 63°(+). In the absence of twinning it was not possible to measure the angle Z ∧ c. The composition according to Seelye's analysis is as follows:—

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Table IV—Analysis of Augite.
Waihola T. augite. Waihola Mol. Prop. Atomic Ratio to 6 (0.0H). (1) (11)
SiO2 45.28 0.754 1.724 2.00 45.56 44.71
Al2O3 7.60 0.075 0.343 0.276
0.067		 8.15 7.85
Fe2O3 2.45 0.036 0.068 2.46 4.46
FeO 7.48 0.104 0.238 5.46 4.23
MgO 10.31 0.257 0.587 11.88 11.74
CaO 22.45 0.401 0.917 22.84 22.37
Na2O 0.60 0.010 0.023 1.02 0.90
K2O 0.07 — — 0.62 0.09
H2O+ 0.26 — — — 0.26
H2O− 0.12 — — 1.98 — 0.09
CO2 nt. fd. — — — —
TiO2 2.88 0.036 0.082 1.87 2.92
P2O5 0.40 — — — — 0.12
V2O3 0.047 — — — — —
S 0.02 — — — — —
MnO 0.18 0.002 0.004 0.42 0.10
NiO tr.
BaO nt. fd. — —
SrO< 0.01
Cl nt. fd.
100.16 100.28 99.84*

[Footnote] * Min. Abstracts, vol. 24, p. 212, gives 100.34.

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Analysis (I) by A. Hueber (in L. Jugovics. Constitution of the Basalt Plateau of Mount Medves and its Crystal Tuff. Mat. Természettud, Ertesitó, Budapest. 1934. Vol. 51, pp. 443–470) is of an augite with sp. gr.=3·31, 2V=57°2′, and Z∧c=45°2′ to 47°5′. A better comparison with the Waihola titanaugite is, however, afforded by (II) a titanaugite from a monzonitic teschenite (W. Wawryk. Sur l'augite commune et titanifère des teschénites en Pologne, Arch. Min. Tow. Nauk. Warszaw. 1935. Vol II, pp. 175–181). On this augite 2V=51°. Z∧c=50°, and α=1·721, β=1·725, γ=1·746; sp. gr.=3·401. The main difference between this and the Waihola titanaugite lies in the higher ratio of Fe2O3 to FeO, though the total iron content remains about the same. It is significant that the higher oxidation of the iron in (II) appears to have caused considerable increase in the refractive indices. The presence of P2O5 in the Waihola augite is attributed to the occurrence of fine needles of apatite within the pyroxene grains, and not to the presence of apatite grains associated externally with the purified (centrifuged) powder. Allowance has been made for the lime associated with the P2O5 in calculating the formula for this augite. On the basis of 6 (O.OH) atoms to the unit cell, the analysis agrees well with the structural formula XY (SiAl)2(O+OH, F)6 suggested by Machatschki (1929) yielding, as shown above, the formula (Mg, Fe”, Fe”′, Al, Ti, Ca, Mn, Na)1.98 [(Si, Al2)O6]. Here the Al is split between the Si and XY groups to satisfy the silicon chains of the pyroxene structure. Although the augite is fairly titaniferous, none of the Si is replaced by it, as apparently can take place in augites high in Ti but low in Al. If the Fe2O3 be calculated as 2FeO and the Al2O3 and TiO2 be ignored, there is not quite sufficient silica to give the formula Wo48En36Fs22 which would correspond with positions on Deer and Wager's (1938) triangular diagrams which otherwise accord fairly well with the optical properties observed.

Apatite separated from the same rock has sp. gr.=3·16±0·01 and ω=1·6370 and ω=1·6339, both ±0·0002. These figures are within the ranges given by Hausen (1929) for the normal apatites. The composition calculated from Seelye's analyses of the Waihola theralites is that of a nearly pure fluor-apatite.

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