Contributions to the Mineralogy of New Zealand—Part V

By C. Osborne Hutton

a-axis zero-layer Weissenberg film. Two lines at d = 1.218 and d = 0.902 Å that result from reflections from (314) and (534) respectively have not been recorded by Swanson et al., although they are both permitted by the space group for zircon, and have been observed on the writer's Weissenberg and powder films.

In one of the powder patterns listed for comparative purposes by Swanson et al., viz. the British Museum pattern, there is a diffuse line at 1.217 Å with an intensity of 20. This has been dismissed by these writers as alone due to monoclinic form of ZrO₂, or baddeleyite. They are justified, in the main, since the British Museum pattern also exhibits a strong line at 2.76 Ź that is undoubtedly due to baddeleyite, but the writer believes that they are incorrect in considering the line at 1.217 Å as solely due to baddeleyite.

Again it should be noted that, although Swanson et al. do not record a line at 0.902 Å ca, the United Steel Companies pattern listed by them does contain this line; the intensity, however, is given as 50 on their scale, although the corresponding reflection due to (534) is faint in both the present writer's powder pattern and a-axis 3rd-layer Weissenberg film. Inspection of the scale of intensities listed with d-spacings by the United Steel Companies, suggests that their films have been heavily over-exposed; this would permit fainter lines to assume greater densities.².

Table. I —X-ray Powder Diffraction Data for Hyacinth

Snowy River, south-western Nelson, New Zealand (x-ray films Nos. 1123, 1124). Nickel-filtered copper radiation (CuK_a = 1.5418 Å). Camera diameter = 114.59 mm; cut-off at 18.5 Å ca. Spacings corrected for film shrinkage. Disordered form:

a_o = 6.625 Å, c_o = 6.010 Å. Ordered form a_o = 6.605 Å, c_o = 5.978 Å.

Samarskite in Hyacinth

Table II —X-ray Diffraction Powder Patterns of Samarskite.

Nickel-filtered copper radiation (CuK_a = 1.5418 Å) Camera. diameter = 114.59 mm. Cut-off at 18.5 Å ca. Intensities determined visually and films corrected for shrinkage.

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Explanation of Table II.

A. Samarskite heated in air to 1130–1140° C. for three hours. Spruce Pine, Mitchell Co., North Carolina . X-ray film No. 255. The lines at 2.517 and 2.497 Å and those at 1.436 and 1.426 Å are bracketed together because these pairs of lines are only barely resolved. Resolution is somewhat less in films yielded by material that has been heated to 1000° C., still less so at 950° C., and was unrecognized in films yielded by samarskite that has been heated to 860° C. (column B).

The line at 1.560 Å represents the sharp shoulder of a band that fades off imperceptibly towards lower angles of 2θ. The band is approximately 0.03 Å in width. A number of very diffuse lines have been noted in the film following the last spacing (1.018 Å) listed.

B. Samarskite as for A, but heated in air to 860° C. for 30 minutes. X-ray film No. 1150. The lines that are bracketed signify barely resolved reflections, and in the case of lines at 1.914, 1.888, and 1.859, although resolution is quite evident, the lines are enveloped in a fairly strong diffuse band.

C. Samarskite inclusion in hyacinth, heated in air to 860° C. for 30 minutes. Snowy River, south-western Nelson, New Zealand . X-ray films Nos. 1130 and 1131A.

Bracketed lines have the same significance as those in columns A and B. The line at 1.431 Å, although rather broad, is not diffuse; it is probably a doublet.

D. Samarskite as for columns A and B, but heated in air at 560° C. for four hours. X-ray film No. 252.

The lines at 1.764 and 1.700 Å constitute a band, rather sharp at 1.764 Å but fading towards higher angles. The lines at 1.490 and 1.440 Å represent the limits of a very diffuse band.

E. Samarskite heated in air to 600° C. for five hours. The locality is given merely as N. Carolina (Lima-de-Faria, 1956, p. 128, Table I, 3rd column).

D, diffuse line. B, broad line. VD or VB, very diffuse or very broad line. VBD, very broad, diffuse line.

The temperature at which hyacinth with inclusions was heated—viz., 860° C., was chosen before it was realized that the inclusion material was samarskite. Accordingly, the x-ray diffraction pattern yielded by the phases so formed by the multiple oxide may not readily be compared to any recorded data, because powder patterns made available by other investigators (Berman, 1955; Lima-de-Faria, 1956, 1958) have been obtained from samarskites heated to temperatures of 600° C. and 1000° C. in air. For this and other reasons, x-ray patterns have been secured for Spruce Pine samarskite that had been heated in air to 560°, 600°, 750°, 860°, 1000° C. 1130–1140° C. The 600° and 1000° C. temperatures were chosen so that the films obtained by the present writer might be compared with the data recorded by Lima-de-Faria, and the other temperatures were chosen after inspection of differential thermal analysis curves of Spruce Pine samarskite. The curve obtained in this instance shows, after an initial endothermic dip, four exothermic peaks at 445°, 700°, 830°, and 1015° C. It would seem appropriate, therefore, to heat specimens of samarskite for subsequent x-ray study at temperatures which correspond to points on the differential thermal analysis curve that indicate a cessation of an exothermic reaction.

It should be noted that for temperatures in excess of 1000° C. a heating period of 30 minutes is quite adequate, and in fact in the study reported later in this paper it is stated that films yielded by euxenite that had been heated to 1000° C. in air for 10, 30, 60 and 180 minutes are identical in every way. A number of specimens of samarskite studied here were heated for a range of periods up to four hours, but careful inspection of the films yielded by materials so treated showed that longer periods of heating were no more effective than the shorter ones.

The x-ray diffraction powder patterns yielded by samarskite heated to 560°, 600°, 860°, and 1130–1140° C. are set out in. Table II, and a number of these are to be found in Pl. 44. The pattern secured for samarskite that had been heated to the latter temperature is listed here in place of that yielded by the same material after heat-treatment at 1000° C., because, although the two patterns are identical,

Euxenite-Polycrase

In heavy residues secured from gravels of the Nile or Waitakere River, just downstream from its junction with Awakari Stream¹, some particles were dismissed, at first, as anhedral grains of chromite or chromian spinel owing to deep brown colour, isotropic character, and marked conchoidal fracture surfaces, until a few

Fig. 3. —Slightly simplified drawings of euxenite-polycrase crystals from the Nile River, New Zealand. Magnification is approximately the same for all crystals, and crystal B is 2.1 mm in length. A and B: Crystals exhibit development of forms a {100}, b {010}, d {101}, and m {110}, together with satellites. Crystals are strongly striated parallel to [001]. C: Two striated crystals of similar form with a {100}, d {101}, and b {010} exhibit inter-penetration effect.

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Explanation to Table III

• A.

  Euxenite-polycrase, Nile River, south-western Nelson, New Zealand. The specimen was heated, as fragments (average diameter = 0.5 mm ca.), in vacuo for one hour at 620° C. X-ray film No. 1034.

  • a.

    Several additional lines are to be observed at higher angles than the last line recorded here, but they are so faint and diffuse that no measurements were made.

• B.

  Euxenite-polycrase, Nile River, south-western Nelson, New Zealand. The specimen was was heated as fragments in air for three hours at 700° C. X-ray film No. 1045.

  • a.

    Strongly asymmetric line.

  • b.

    In comparison to the lines at higher and lower angles, this line is very precisely defined.

  • c.

    A. few additional lines are to be observed at higher angles than the last line recorded here, but they are extremely faint and very diffuse.

  • d.

    The lines from 1.34–1.03 Å are measured only approximately owing to the diffuseness of the reflections.

• C.

  Euxenite, south Norway. The specimen was heated in air to 700° C. for three hours (Lima-de-Faria, 1958, p. 938, Table I).

• D.

  Euxenite-polycrase, Nile River, south-western Nelson, New Zealand. The same specimen that yielded the pattern listed in column A of this table was heated as a fragment (0.1 mm in diameter ca.) in vacuo for 1¾ hours at 1130–1140° C. X-ray film No. 1036.

  • a.

    This is a broad band with a wide shoulder on the higher 2° side.

  • b.

    A slight shoulder on the high 2° side.

• E.

  Euxenite, Iveland, Setesdalen, Norway. The specimen was heated as fragments in air for 2¼ hours at 1130–1140° C. X-ray film No. 215.

  • a.

    This is a broad band of uniform density.

  • b.

    The 1.817 Å reflection consists of a sharp line superimposed upon a diffuse band that ranges from 1.802–1.825 Å. This situation is distinct from the more precisely defined lines at 1.814 and 1.834 Å in column D of this table.

  • c.

    The absence of a corresponding strong line in the pattern presented in column D of this table appears to be one of the outstanding differences between the patterns in columns D and E.

  • d.

    These two lines represent the two relatively sharp edges of a diffuse band; the latter is not evident in the pattern in column D, but instead two precise lines are present.

  • e.

    These lines represent the two relatively well-defined edges of a diffuse band. Resolution into two distinct lines has occurred in the pattern in column D of this table.

  • f.

    A broad diffuse band.

• F.

  The d-spacings listed here are the calculated values for euxenite-polycrase in column D in this table.

The letters in the intensity columns, B, VB, BD, VBD and D, indicate broad, very broad, broad and diffuse, very broad and diffuse, and diffuse lines respectively.

• a.

  Morphological axial ratio after W. C. Broegger.

• b.

  Ratio derived from x-ray data.

• c.

  Nefedov has a_o = 5.18, b_o = 14.70, c_o = 5.72Å, and this order does not correspond with the axial ratio derived therefrom by him; the present author has transposed Nefedo's values for a_o and c_o.

• d.

  Determined by single crystal work.

• e.

  Ratio derived from x-ray data and to be compared with morphological ratio already given—viz. a:b:c = 0.369:1:0.348.

The x-ray powder patterns obtained with Nile River material, after having been heated to 620°, 700°, and 1130–1140° C., are set out in Table III, columns A, B, and D, and the d-spacings of the two latter specimens are compared to those recorded by Lima-de-Faria (1958, pp. 938–939) for euxenite that had been heated

to 700° C. (Table III, column C), and to data obtained by the present writer for Setesdalen, Norway, euxenite¹ that was subjected to a temperature of 1130–1140° C. in air (Table III, column E). The d-spacings yielded by the Nile River sample and the Norwegian material, both of which have been heated to 1130–1140° C., are quite comparable, and any slight differences that do exist possibly result merely from compositional variation between the two specimens.² Furthermore, the similarities between the powder patterns yielded by Nile River euxenite-polycrase that had been heated to 700° and 1130–1140° C. are quite striking. Lima-de-Faria's x-ray pattern obtained from euxenite that had been heated to 700° C. is listed in Table III, column C, for the sake of comparison, and there is little obvious similarity between the latter and Nile River euxenite that had been heated to the same temperature. The only line in Lima-de-Faria's pattern that corresponds reasonably well is the most intense line at 2.92Å, but as for the other lines, if the d-spacings should correspond approximately, the intensities are out of all proportion to those listed in column B; note, for instance, the line at 1.79 Å (Table III, column C) with an intensity of 7, or 70 when compared with the same scale employed in column B, and the line at 1.77 Å in the latter column.

Accordingly, Lima-de-Faria's pattern of euxenite (Table III, column C) is much more comparable to that yielded by Pilbara, Western Australia, tanteuxenite, for instance, where a face-centred cubic pattern (uraninite or pyrochlore-microlite type) is obtained after the material has been heated to about 700° C. After a study of films yielded by a large number of specimens of euxenite that had been heated to about 700° C., the uraninite or pyrochlore-microlite type of pattern appears to be only occasionally developed. Instead, a pattern similar to that set out in Table III, column B, is the type more often obtained.

According to the studies of Komkov (vide Nefedov, 1956, p. 85) “the x-ray pattern of anisotropic euxenite is identical with that of the regenerated or heat-treated euxenite”. This statement is presumed to indicate that the powder patterns of anisotropic euxenite and of the heat-treated metamict mineral are identical. Nefedov (1956) found that similar circumstances obtained for an anisotropic euxenite from the Central Ural Mountains. Accordingly, determination of the dimensions of the unit cell of euxenite from the powder pattern of a heat-treated but originally completely metamict mineral would appear to have some value. The cell dimensions of the Nile River euxenite-polycrase have been calculated from the powder pattern after partial indexing of the more critical reflections (Table III, column F), and are as follows: a_o = 5.53, b_o = 14.63, c_o = 5.16 Å, which leads to an approximate x-ray axial ratio a: b: c: = 0.378:1:0.353.

These data may be compared with the unit cell dimensions of euxenite that are recorded by other writers, in Table IV.

Acknowledgments

The writer wishes to acknowledge the opportunities provided for this research by the award to him of a John Simon Guggenheim Foundation Fellowship during 1953–1954, and he is also indebted to the Shell Fund for Fundamental Research