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Volume 88, 1960-61
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Contributions to the Mineralogy of New Zealand—Part V

[Read before the Otago Branch, April 12, 1960; received by the Editor, May 19, 1960.]

Abstract

Hyacinth and samarskite from Snowy River, and euxenite-polycrase from Nile River, south-western Nelson, New Zealand, have been studies in some detail.

Two distinct morphological developments have been noted for hyacinth with m {110} and p {111}, or a {100} and e {101} as apparently sole forms. Single-crystal rotation photographs of unheated hyacinth exhibit the results of disordering, but heating at 760° C. for 15 minutes, either in air or in vacuo, restores order. Physical constants determined for hyacinth are: (for disordered forms) a0 = 6.625 Å, c0 = 6.010 Å, ± 0.002 Å, cell volume = 263.782 Å3; sp. gr. at 20° C. (meas.) = 4.58, ± 0; 01; (for ordered forms) a0 = 6.605 Å, c0 ± 5.978 Å, ± 0.002 Å, cell volume = 260.796 Å3; sp. gr. at 20° C. (meas.) = 4.63, ± 0.01. Indexed powder patterns for both forms are recorded.

Occasional crystals of hyacinth with metamict samarskite as inclusion-material have been found which, after appropriate heat-treatment, yield single crystal photographs of ordered zircon with a powder pattern due to samarskite superimposed thereon. New Zealand and Spruce Pine, North Carolina, samarskite have been heated over a range of temperatures and under a variety of conditions, and the powder patterns obtained from these products are listed fully, and compared in some detail to data obtained by other writers.

Fragmentary crystals of euxenite-polycrase with n = 2.2–2.25, and sp. gr. just less than 5, are very rare constituents of heavy concentrates obtained from Nile River gravels. The forms a {100}, b {010}, c {001}, d {101}, and m {110} have been recognized with certainty in crystals that are strongly striated and prismatic parallel to [001], and flattened parallel to {010}; satellites are present in some cases. The mineral is completely metamict, and after heat-treatment over a range of temperatures, and under a variety of conditions, distinctive x-ray powder patterns have been obtained. Unit cell dimensions, calculated from powder data secured by heating the mineral to 1130–1140° C. are: a0 = 5.53, b0 = 14.63, c0 = 5.16Å. Inter-axial ratio a:b:c = 0.378:1:0.353 (from x-ray data), and 0. 369:1:0.348 (morphological ratio).

Hyacinth

In heavy concentrates obtained from the Snowy River dredge and stream gravels of that south-western Nelson river, the variety of zircon known as hyacinth is one of the more important constituents along with ilmenite, monazite, xenotime, and garnet. Attention has been drawn to the morphology and physical properties displayed by this mineral in an earlier paper (Hutton, 1950, pp. 689–692), but additional data are now reported.

Single crystal study of the least abraded particles of the simplest form, 0.062–0.125 mm in length, shows that in seven crystals, the forms m {110} and p {111} are dominant, with a {100} apparently absent. On the other hand, the remaining three crystals exhibit a {100} and e {101} as the dominant forms with m {110} and p {111} apparently not developed. The development in zircon of second order prisms as the sole form in the zone [001] would appear to be unusual.

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Films yielded by rotations about the a- and c- crystallographic axes of carefully oriented crystals1 exhibit reasonably precise reflections at low angles on the zero-and first-layers, but at angles greater than 80° 2θ, the reflections on the zero-layer become diffuse and there is no resolution into α1 and α2 lines. Third-layer lines in films for both a- and c- axis rotations are barely visible, and the reflections therein are merely diffuse streaks 3–4 mm in length (compare Fig. 1A, Plate 43, with Pabst, 1952, p. 155, top illustration in Fig. 6).

From zero-layer Weissenberg films that have been calibrated with quartz, unit cell dimensions of hyacinth have been determined to be as follows: ao = 6.625 Å, co = 6.010 Å (cell volume = 263.782 Å3), and both values are considered to be subject to error not in excess of 0.002Å.

Owing to the need to preserve the measured crystals undamaged for subsequent heat-treatment, powder photographs of hyacinth were obtained from crystals that exhibited similar hue and tone to those employed in single crystal work. A typical powder pattern, set out in Table I, column A, has been indexed as fully as possible in spite of the diffusitivity of reflections at higher angles2, and the lines therein do not exhibit any degree of asymmetry comparable to the skewing of peaks observed by Hurley and Fairbairn (1953, p. 665).

Crystals for which cell dimensions had been obtained, were then heated in silica capillaries in vacuo, and also in air, at 760° C. for 15 minutes.3 From a superficial point of view, the only effect of this treatment was decolouration of the crystals, but x-ray films secured for a- and c- axes rotations are distinct from those obtained before such treatment on account of the degree of ordering that had then taken place. The reflections are precisely defined, resolution into α1 and α2 reflections is evident, and the third-layer in films of both orientations is clearly developed (for copper radiation). No powder arcs are present except in rare cases to be described later in this paper, and accordingly, the situation for hyacinth employed herein is distinct from that found by Pabst (1952, p. 154) for Indiahoma, Oklahoma, zircon with a much greater degree of metamictization, but comparable to that found by von Stackelberg and Chuboda (1937), and von Stackelberg and Rottenbach (1940) for only partially altered zircon.

Careful measurements of a- and c- axes zero-layer Weissenberg films, standardized by quartz, gave cell dimensions as follows: a0 = 6.605 Å, c0 = 5.978 Å (cell volume = 260.796 Å3); the cell dimensions were found to vary by no more than 0. 002 Å in measurements made with several films.

As in the case of the unheated hyacinth crystals, the heat-treated material has been retained, and powder patterns prepared from other, but strictly comparable, crystals that were subjected to similar heat-treatment.

A typical powder pattern of the ordered form is set out in Table I, column B; this has been fully indexed, and at the same time, calculated d-spacings that correspond to all reflections observed on Weissenberg films have been listed. A few reflections such as (444), present in the powder pattern, but lying in blind areas between the a- and c-rotation axes, have been found on films secured by rotation about [110].

This pattern compares satisfactorily with that recorded by Swanson, Fuyat, and Ugrinic (1955, p. 71), although several additional faint lines are recorded by the present writer; one line observed by Swanson et al., viz. d = 0.853, was not found on the powder film, but the corresponding reflection was observed on the

[Footnote] 1 Rotation and crystallographic axes do not depart from one another by more than 5 minutes.

[Footnote] 2 The corrected diffraction angle (2θ) for the line due to (112) is 35.47, and according to Hurley and Fairbairn (1953, p. 666, Fig. 2), the hyacinth studied here would appear to have an activity equivalent to about 160 alphas/mg/hr.

[Footnote] 3 Heating, either in air or in vacuo, produces similar results, and no differences in cell dimensions were detected in hyacinth treated by the two methods.

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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 Å1 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 (CuKa = 1.5418 Å). Camera diameter = 114.59 mm; cut-off at 18.5 Å ca. Spacings corrected for film shrinkage. Disordered form:

ao = 6.625 Å, co = 6.010 Å. Ordered form ao = 6.605 Å, co = 5.978 Å.

A B
hkl d. calc. d. meas. I d. calc. d. meas. I
101 4.4615 4.47 50 4.439 4.43 50
200 3.3143 3.315 100 3.305 3.29 100
211 2.658 2.662 10 2.649 2.647 15
112 2.529 2.53 60 2.517 2.518 60
220 2.343 2.34 15 2.337 2.333 25
202 2.226 2.226 10 2 .165 2.216 20
301 2.073 2.072 30 2.066 2.066 35
103 1.918 1.919 15 1.907 1.913 25
222 1.8405
321 1.757 1.757 15 1.751 1.750 25
312 1.719 1.720 40 1.7125 1.710 50
213 1.652
400 1.6565 1.656 15 1.651 1.650 35
411 1.553 1.549 2 1.548 1.544 5
004 1.503 1.506 3 1.495 1.495 5
303 1.478
420 1.4815 1.480 10 1.4775 1.475 25
402 1.446
332 1.386 1.386 15 1.381 1.380 35
204 1.368 1.368 8 1.362 1.364 20
323 1.349
422 1.324
501, 431 1.294 1.292 5 1.290 1.289 15
224 1.265 1.266 6 1.259 1.262 20
413 1.253 1.251 1 1.2485 1.248 3
314 1.215 1.218 1D

[Footnote] 1 The low-angle lines in the British Museum pattern all appear to have d-spacings that are too low; accordingly, the 2.76 Å line almost certainly corresponds to that at 2.84 Å in baddeleyite.

[Footnote] 2 In this connection note that the (312) line at 1.71 Å in the United Steel Companies pattern is given an intensity of 100, whereas in carefully exposed Weissenberg films, it is less than one half the density of the reflection due to (200).

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521 1.193 1.191 8 1.200 1.201 1D
512 1.189 1.189 30
105 1.177
440 1.171 1.171 <1D 1.168 1.167 5
215, 404 1.113 1.113 2 1.108 1.110 10
503, 600, 433 1.104 1.104 3D 1.101 1.1015 10
611 1.072 1.069 1.068 1
532 1.063 1.062 4D 1.059 1.059 15
424, 305 1,055 1,054 4D 1.051 1.052 15
523, 620 1.048 1.047 3D 1.045 1.045 8
541 1.0165
325 1.006 1.006 1D 1.001 1.003 1
622 .986
116 .979 .979 2D .974 .9765 5
631 .974 .9715 .971 2
415 .962 .958 .958 1
206 .954
613 .957 .9535 .9535 2
701 .932 .932 2
444 .920 .9215 5
640 .9165
543 .916 .916 10
534 .903 .902 5
316 .899 .899 1
721 .897
712, 552 .892 .892 20
604, 505 .887 .886 2
633 .883
525, 624 .856 .857 20
703, 406 .853
107 .847
336 .839
651 .837
732 .833 .833 25
800, 723 .826 .825 3
217 .821
811, 741 .812 .812 3
615 .805
820 .801 .801 .5
307 .7965
802 .792 .792 30D
516 .790
644 .781 .781 30D
563 .7785
237 .774
822 .773

A. Disordered form of hyacinth.

B. Ordered form of hyacinth after having been heated to 760° C. for 15 minutes in air or in vacuo.

I = Intensities were determined visually. D = Diffuse reflection.

The unit cell dimensions of heat-treated Snowy River hyacinth are almost identical to the values recorded by Swanson et al. (1955, p. 69) for zircon. Constants determined for hyacinth are as follows: ao = 6.605 Å and co = 5.978 Å, and these data are to be compared to ao = 6.604 Å and co = 5.979 Å for the exceedingly pure zirconium silicate employed by the National Bureau of Standards for their measurements.

Specific gravities have been determined for natural hyacinth and the heat-treated mineral, but it must be stressed that these data have not been observed for the actual crystals for which cell dimensions have been measured, but instead,

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Fig. 1. —c-axis rotation photographs of hyacinth from Snowy River. south-western Nelson. New Zealand. Nickel-filtered copper radiation and camera diameter = 57.29 mm.
A (upper). Hyacinth before heat-treatment. X-ray film No. 1038.
B (lower). Hyacinth after having been heated in air for 30 minutes at 860° C., with a superimposed powder pattern due to recrystallized samarskite inclusion. This powder photograph may be compared to that illustrated in Fig. 2C. X-ray film No. 1130.

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Fig. 2.—X-ray diffraction powder patterns of samarskite. Nickel-filtered copper radiation (CuKa = 1.5418 Å). Camera diameter = 114.59 mm. Cut-off = 18.5 Å ca.
A. Heated in air to 600° C. for 30 minutes. Exposure time = 5.3 hours, aperture No. 3. Film No. 1154. Spruce Pine. Mitchell Co., North Carolina.
B. Heated in air to 860° C. for 30 minutes. Exposure time = 5.6 hours, aperture No. 1 Film No. 1150. Spruce Pine, Mitchell Co., North Carolina.
C. Inclusion material from hyacinth. Heated in zircon in an to 860° C. for 30 minutes. Exposure time = 4.9 hours, aperture No. 3. Film No. 1131. A Snowy River. Mawheraiti S.D., south-western Nelson, New Zealand.
D. Heated in air to 1000° C. for 30 minutes. Exposure time = 5.3 hours, aperture No. 4. Film No. 1155. Spruce Pine, Mitchell Co., North Carolina.
E. Inclusion material removed from hyacinth and heated in air to 1000° C. for 30 minutes. Exposure time = 6.0 hours, aperture No. 4. Film No. 1134. Snowy River, Mawheraiti S.D., south-western Nelson, New Zealand.

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10–15 mgm amounts of carefully hand-picked hyacinth crystals were used. These data are as follows:

Natural Hyacinth Heat-treated Hyacinth
Sp. gr. meas. at 20° C. 4.58 ± 0.01 4.63 ± 0.01
Sp. gr. calc. from cell dimensions 4.585 4.638

Samarskite in Hyacinth

In nearly pure samples of hyacinth from Snowy River concentrates several crystals were observed to have brown inclusions, and in the past one has only attempted to make an informed guess as to their precise nature (Hutton, 1950, p. 690).

Efforts have been made to identify these inclusions by single crystal x-ray studies in which hyacinth crystals have been carefully oriented for rotation about either the a- or c-crystallographic axis. In most cases crystallographic axes of inclusion-material have been so misaligned with respect to the axes of the zircons being investigated, that the array of reflections due to inclusions could not be interpreted. In those instances where an axis of an inclusion approached parallelism either to the a- or c-axis of zircon it was possible to determine the nature of the inclusion. In this way, apatite, monazite, and zircon have been recognized with certainty. This procedure, however, did not provide a technique that was any better than more simple and speedier methods.

The situation with rare brown, apparently isotropic inclusions, was different; and rotation films exhibit only reflections due to zircon. Acting upon the assumption that such material may be in a metamict condition, the hyacinth containing such inclusions was heated in air for 30 minutes at 860° C. These crystals, when carefully oriented with the c-axis as rotation axis, yield rotation patterns of well-ordered zircon, but in addition, a fairly precisely defined, but rather faint, powder pattern (PI. 43B, lower) becomes evident. Measurement of the powder pattern suggests that the material may be samarskite, but the desired precision was not attained owing to the diameter of the camera employed (57.29 mm), and the faintness of the lines in most cases. Longer exposure times did not resolve the latter problem, because the intensity of the background became too great. Accordingly, as it was being observed beneath a binocular microscope, the crystal of hyacinth was carefully fractured between glass slides in a smear of glycerol, and the inclusion material, which had a bread-crust aspect, was found to be incoherent, and fell to a fine powder. After removal of glycerol, as much of the powder as possible was picked up in a vaseline-smeared glass hair, and mounted in a 114.59 mm camera; this specimen was found to yield good powder patterns that permitted reasonably precise measurement (PI. 44C).

These data are set out in Table. II, column C, and are compared there with powder data yielded by undoubted samarskite from Spruce Pine, Mitchell County, North Carolina (Table II, columns A, B, and D; also Fig. 2, PI. 44). The d-spacings and intensities listed in Column B are those yielded by samarskite that has been subjected to treatment identical to that accorded samarskite in hyacinth, and it will be observed that the d-spacings and intensities listed in B and C are quite similar.

A number of distinctive points are evident, however, and perhaps the most obvious one concerns the line with maximum intensity. For inclusion material, the strongest line is found at 3.20 Å, whereas the line with a comparable spacing in Spruce Pine samarskite is rated at 70 ca.; on the other hand, the most intense reflection in the latter specimen is to be found at 2.90 Å.

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

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

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

A B C D E
d. meas. I d. meas. I d. meas. I d. meas I d. meas. I
6.06 1VD
4.16 2
4.01 30 4.02 50 4.02 40B
3.76 10
3.56 10 3.56 10 3.58 10 3.64 3D 3.62 1
3.22 25 3.22 70 3.20 100VB 3.20 1
3.19 1D 3.12 10D 3.13 1
3.10 30D 3.04 5 3.06 40
2.98 30 2.98 30 2.99 50 2.98 100BD 2.97 10B
2.945 5D
2.89 100 2.90 100 2.91 45
2.806 1 2.805 1 2.80 5D 2.80 1
2.784 5 2.748 5 2.751 5
2.735 10
2.633 1
2.574 5D 2.589 5 2.592 10 2.583 10D 2.58 4
2.517 40D 2.508 50BD 2.500 70
2.497 40D
2.438 20 2.443 10D 2.467 5D
2.317 10 2.327 1D
2.260 1
2.213 5
2.160 10 2.165 5D 2.165 1D 2.187 <.1D
2.050 10 2.053 5D
2.006 10 2.009 5D 2.008 1VD
1.900 40D 1.914 20VD 1.901 10
1.870 15 1.888 5VD 1.887 10 1.896 5D 1.89 1
1.852 20 1.859 30VD
1.827 30 1.836 10D 1.836 40 1.828 20D 1.82 8
1.790 5D 1.7905 1D
1.752 1D 1.764 1.75 1
1.730 25D 1.734 15D 10
1.705 60 1.707 40 1.705 30D 1.700
1.686 55 1.683 40 1.682 20D
1.647 5 1.648 1D
1.636 1VD
1.623 10VD
1.576 30D
1.560 50D 1.570 40VBD 1.566 40D 1.563 5D 1.56 8
1.513 30D 1.508 15VBD 1.490 1.49 1
1.456 5D 1.460 1D 1VD
1.436 30 1.440
1.431 30BD 1.431 20
1.426 5D
1.372 1D 1.371 1D
1.350 5D 1.352 2D 1.357 1VD 1.355 1VD 1.35 1
1.2935 1D 1.292 2D 1.300 1VD 1.287 1
1.264 1D 1.260 1D 1.267 1VD
1.238 1D
1.224 5D 1.223 5D 1.223 1VD
1.190 5VBD 1.194 5D 1.190 1VD 1.193 <1VD 1.184 5
1.168 2D 1.171 5D
1.159 1D 1.1605 2D 1.159 1VD 1.154 5
1.148 1D
1.118 2D 1.117 1VD
1.112 1VD
1.1065 1D
1.091 1D 1.090 1VD 1.084 1VD
1.079 2VD 1.078 2VD
1.058 2VD 1.041 1VD 1.034 1VD 1.053 3
1.018 2VD 1.019 1VD
1.000 5VD 1.000 1VD .994 3
.977 1VD
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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,

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a very slight improvement in resolution in the film for the mineral treated at the higher temperature is evident. Doubtless this increase in resolution is to be correlated with the relatively weak exothermal reaction that takes place at 1015° C.

The d-spacings in column A are comparable to those reported by Lima-de-Faria (1956, p. 128, Table I) for samarskite that had been heated to 1000° C., except upon two accounts: (1) the present writer has recorded a considerable number of additional lines, and (2) the intensities reported by Lima-de-Faria at higher angles of 2θ are, in most instances, very much in excess of those found by the present writer, a situation that may be the result of excessive over-exposure of films by Lima-de-Faria. This would seem to be quite definitely the situation with Lime-de-Faria's Boa Esperança samarskite, since he records ten lines with intensities equivalent to 10 (100 on the present writer's scale), and four of them have d-spacings less than 1.180 Å.

The patterns yielded by Spruce Pine samarskite that had been subjected to temperatures of 600° C. for four hours are identical to those for material treated at 560° C. (Table II, column D), and are comparable in a general way only, with Lima-de-Faria's pattern for similarly treated samarskite from the same locality (Table II, column E). Lima-de-Faria has listed intensities that are approximately one-half to one-third that of the most intense line at 2.97 Å for many reflections at angles greater than about 80° 2θ; these intensities appear to be excessive, and it is tentatively suggested that that author's films are much over-exposed.

In commenting upon the results of heating samarskite in air, Lima-de-Faria (1956, p. 127) states that “practically all the strong arcs obtained on heating at 600° C. are hardly noticeable after heating at 1000° C.”. While it is true that an additional phase, or phases, may result from heating at 1000° C. compared to the material produced at 600° C., it seems to the present writer that Lima-de-Faria's statement creates the impression that the x-ray diffraction patterns yielded by samarskite subjected to these different heat-treatments have little in common with each other. This is not strictly the picture that emerges as one examines films yielded by material heated to 560°, 750°, 860°, and 1140° C. when these are laid side by side in that sequence. Most of the broad, diffuse lines found in films of samarskite that had been heated to 560° C. gradually become resolved into separate lines that are fairly closely spaced but precisely defined in films yielded by material heated to the higher temperatures. Note, for instance, the situation as it applies to lines at 2.98, 2.80, and 2.583 Å in d-spacings yielded at the lowest temperature employed here (Table II, column D). Furthermore, the diffuse line of medium strength at 1.896 Å (Table II, column D) corresponds to a broad band of great diffuseness in which three rather well defined lines are visible in samarskite heated to 860° C. (Table II, column B), whereas at the highest temperature the diffuse background virtually disappears and the precisely defined lines remain. Comparable situations are evident at other points on the films.

In a later paper on the effects of heat-treatment of metamict minerals, Lima-de-Faria (1958, p. 940) states that in his experiments he has adopted the practice of heating the powdered minerals rather than fragments thereof. He believes that oxidation, if it should occur, would be more complete in the case of powders, instead of being restricted to peripheral zones of fragments. Lima-de-Faria does not give any indications of the minimum dimensions for fragments that might be affected in this way, but the present writer's experience, so far as samarskite is concerned,

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shows that if particle diameters of mineral grains to be subjected to heat-treatment average about 0.1 mm then the x-ray diffraction pattern yielded by a single particle of this size is identical with that obtained from material that had been finely powdered before heat-treatment. Furthermore, oxidation may not be an important factor, because the North Carolina samarskite when heated either in air or in vacuo yields x-ray diffraction patterns that cannot be distinguished one from the other.

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

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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.

[Footnote] 1 Situated in Waitakere Survey District, Nelson Land District.

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fragments were found that exhibit a decidedly non-isometric habit and a refractive index of 2.2–2.25. A close study of the crystal fragments suggested that the mineral might be one of the multiple oxides of tantalum, niobium, and titanium, because the simple form is similar to illustrations of crystals of euxenite-polycrase, samarskite, and delorenzite1 (Palache, Berman, and Frondel, 1946, pp. 788, 797 and 808).

Although material was insufficient to allow specific gravity to be determined precisely, the fragments were found to sink with difficulty, as did pyrite, in a melt yielded by equal molecular proportions of thallous formate and malonate that had been maintained at 75° C. Since such a liquid has a density of approximately five, the probability that the mineral under consideration is samarskite may be dismissed, and instead, the Nile River mineral would appear to a member of the euxenite-polycrase series.

For particles in which some traces of original form are preserved a simple orthorhombic symmetry is evident (Fig. 3). They are prismatic parallel to [001], and, if given an orientation analagous to that adopted for euxenite-polycrase, they are flattened parallel to b {010}. Although a moderate amount of abrasion is evident, {h01} and {hk0} forms are recognized; the front pinacoids are rounded and strongly striated parallel to [001]. It is not clear if the rounding in this case is alone due to the effects of abrasion, or whether the latter circumstance has camouflaged the development of a number of very narrow {hk0} forms; only one {hk0} form was recognized with any certainty—viz., m {110}. Measurement of the angles (100) ∧ (010), (100) ∧ (101), and (100) ∧ (100) gave values of 90°, 47°, and 20° 30′ respectively, and, due to striations and the degree of abrasion present on all crystal fragments, these values are probably subject to an error of about ± 15′, These angles lead to an interaxial ratio a:b:c = 0.369:1:0.348.

One partial crystal exhibits a second but much smaller crystal attached thereto, with a-axes coincident, but with the c-axes at an angle of about 7–8° to one another (Fig. 3B), whereas a second partial crystal displays a small satellite in parallel position with its host (Fig. 3A).

A fragment was set up for single crystal x-ray work, but no diffraction pattern was obtained. Upon heating at different temperatures, however, the products so formed were found to yield good powder patterns that are comparable to those observed for undoubted euxenite-polycrase. A variety of conditions and temperatures was chosen in order (1) to facilitate comparison with data recorded elsewhere, (2) to determine if any diverse effects result from heating samples in air, rather than in vacuo, (3) to observe whether the heat-treatment of powdered samples resulted in changes not observed when unpowdered material was employed, and (4) to determine if the duration of heat-treatment was critical.

With regard to the conditions noted under (2) above, it was found that no differences were to be observed in films yielded by materials heated at a fixed temperature in air or in vacuo. Furthermore, no distinctions were to be observed in the x-ray films if particles, rather than finely crushed powders, were subjected to heat-treatment. Finally, the films yielded by specimens, powdered or particles, that had been heated at 1000° C. in air for periods ranging from 10 to 60 minutes, are identical, whereas if temperatures are held for three hours at 1130–1140° C. the writer has observed only very slight improvement in line resolution (vide Sokolova, 1959, p. 417). Accordingly, only a short period of heating appears to be required in order that the phase or phases stable at a particular temperature may develop, but it must be remembered that long periods of heat-treatment, up to 100 hours, appear to cause a distinct lowering of specific gravity (vide Arnott, 1950, p. 398).

[Footnote] 1 Studies by Butler and Embrey (1959) have shown delorenzite from the type locality of Craveggia, Piedmont, Italy, to be identical to tanteuxenite.

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Table III.—X-Ray Diffraction Patterns of Euxenite-Polycrase.
Nickel-filtered copper radiation (CuKa = 1.5418 Å). Camera diameter = 114.59 mm. Cut-off at 18.5 Å ca. Intensities determined visually and A, B, D, and E are corrected for film shrinkage. Cell dimensions for material with d-spacings listed in D: ao = 5.53, bo = 14.63, co = 5.16 Å, ± 0.03 Å.
A B C D E F
d. meas. I d. meas. I d. meas. I d. meas. I d. meas. I d. calc. hkl
4.56 < 1D 4.74 20 7.21 1 7.07 1 7.31 020
3.64 < 1D 3.64 5D 6.33a 1 6.18—5.78a < 1
3.44 25 3.45 35
3.345 20 3.345 25 5.17 < 1D 5.16 < 1D 5.16 110
2.97 100 2.975 100BD 2.92 10 3.645 40 3.62 40 3.66 3.65 130 040 111
2.94 1
2.785 40D 2.786 30 3.35 10 3.325 10 3.37 121
2.679 < 1D 2.97 100 2.96 100 2.98 131, 041
2.590 5 2.590 1 2.92 5
2.530 5 2.533 5D 2.53 4 2.768 30 2.75 30 2.765 200
2.472 5 2.473a 10 2.618 < 1 2.626 141
2.440 1 2.595 1D
2.295 < 1 2.290 5D 2.589 50 2.573 35 2.584 2.580 220, 150 002
2.181 < 1D 2.1895 2D 2.545 5 2.545 5D 2.541 012
2.101 < 1D 2.116 1D 2.484 < 1
2.055 20 2.039 15 2.439 20 2.431 15 2.438 2.437 060 201
2.000 1D 2.413 20 2.4055 20 2.432 022
1.986 < 1D 1.972 1? 2.333 1D 2.339 102
1.923 20 1.9245 5D 2.313 221, 151
1.893 15 1.898 1D
1.878 15 1.876 8D 2.297 15 2.293 15 2.309 112
1.821 10 1.823 5D 2.281 032
1.769 5 1.7705 1D 1.79 7B 2.226 122
1.723 5BD 1.718 10BD 2.201 10 2.192 15 2.206 240
1.637 5BD 1.636 25VBD 2.182 10 2.166 15 2.180 231
1.573 5BD 1.582b 8 1.53 7B 2.109 40 2.099 30 2.109 132, 042
1.486 5BD 1.492 10VBD 1.46 1VB
1.383 5BD 1.385 2VBD 2.047 161
1.270 1BD 1.34d 1VBD 1.269 1VB 2.029 241
1.160 1BD 1.32 1VBD 1.966 2 1.961 5 1.971 1.955 142 170
a 1.27 2VBD 1.930 3 1.930 5 1.938 052
1.23 1VBD 1.892 45 1.888 45 1.887 202
1.17 1VBD 1.164 2VB 1.859 < 1
1.095 1VBD 1.135 2VB 1.834 20
1.05 1VBD 1.817b 50 1.829 1.828 1.827 310, 260, 080 171
1.03 1VBD 1.034 2VB
c 1.814 50 152, 222
1.766 50 1.765 50 1.772 062
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D E D E
d. meas. I d. meas. I d. meas. I d. meas. I
1.728 30 1.7245 40 1.2415 < 1D 1.242 < 1D
1.719 30 1.7125 40 1.222 30D 1.221d 25D
1.692 < 1 1.207 25D 1.203d 20D
1.677 5 1.674 5 1.184 20D 1.185 25D
1.639b 60 1.634 50 1.172 20D 1.172 30D
1.620 < 1 1.6175 2 1.161 40D 1.1615° 40D
1.608 2 1.6045 5 1.152 20D 1.152° 20D
1.582 1D 1.580 2D 1.1425 1D
1.563 50 1.558 30 1.118 2D 1.117 2D
1.541° 25 1.1085 < 1D 1.108 < 1D
1.503 1 1.501 1 1.100 1D 1.098 1BD
1.492 2 1.4895 2 1.084 2D 1.083 2BD
1.481 60 1.481 60 1.079 5D 1.079 5BD
1.460 10 1.458 10 1.0555 2BD 1.057′ 1BD
1.434 30 1.4345 30 1.046′ 2BD
1.3905 < 1D 1.391 < 1D 1.030 1D 1.030 1D
1.362 < 1D 1.364 < 1D 1.018 40BD 1.017 40B
1.333 5BD 1.335 5BD .998 1BD .997 1BD
1.309 1D 1.308 1D .988 2D .986 10BD
1.291 2D 1.2905 2D .980 1D
1.2755 2D 1.276 2D .9625 25BD .962 20BD
1.257 < 1D 1.257 < 1D .939 20BD .939 20BD
.916 25BD .916 25BD
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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.

Table IV.—Axial Ratios and Unit Cell Dimensions of Euxenite.
Axial Ratios ao bo co Reference
0.3789:1:0.3527a Palache, Berman and Frondel, 1946, p. 787.
0.3789:1:0.3546b 5.520 17.57 5.166 Å Arnott, 1950, p. 397
0.388 :1:0.352b 5.72 14.70 5.18 Åc Nefedov, 1956, p. 85
5.57 14.65 5.18 Åd Sokolova, 1959, p. 417
0.378:1:0.353e 5.53 14.63 5.16 Å Hutton, this paper
  • a.

    Morphological axial ratio after W. C. Broegger.

  • b.

    Ratio derived from x-ray data.

  • c.

    Nefedov has ao = 5.18, bo = 14.70, co = 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 ao and co.

  • 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

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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: ao = 5.53, bo = 14.63, co = 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

[Footnote] 1 Differential thermal analysis of the Norwegian material shows two endothermic dips, a broad one at 200–300° C., and a sharp one at 515° C. These are followed by four exothermic peaks; a minor one at 700° C., an exceedingly strong one at 750° C., and two minor peaks at 870° and 1035° C.

[Footnote] 2 The powder pattern yielded by euxenite that was heated to 900–1200° C. and recorded by Sokolova (1959, Table IV, p. 416) is very similar to that found for Nile River material, and leads to unit cell dimensions close to those found for the New Zealand mineral (Table IV).

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for a grant to purchase accessory equipment to facilitate experiments in heat-treatment of minerals.

Any acknowledgment would be incomplete without grateful reference to the assistance offered by Dr. Frederick G. Tickell.

Bibliography

Arnott, Ronald J., 1950. X-ray diffraction data on some radioactive oxide minerals, Amer. Mineral., 35, 386–400.

Berman, J., 1955. Identification of metamict minerals by x-ray diffraction, Amer. Mineral., 40, 805–827.

Butler, J. R., and Embrey, P. G., 1959. Abstract in Mineral. Soc. Notice No. 104 of January 19, 1959.

Hutton, C. Osborne, 1950. Studies of heavy detrital minerals, Geol. Soc. Am. Bull., 61, 7, 635–716.

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Lima-De-Faria, J., 1956. The standard thermal treatment in the identification of metamict minerals by x-ray powder patterns, Museo e Laboratório Mineralógico e Geol., Fac. Ciências, Univ. de Lisbon, Bull. 24, 7, 125–131 (a different pagination has been employed in reprints of this paper).

Lima-De-Faria, J.,1958. Heat-treatment of metamict euxenites, polymignites, yttrotantalites, samarskites, pyrochlores, and allanite, Mineral Mag., 31, 242, 937–942.

Nefedov, E. I., 1956. New data on fergusonite and euxenite, Information Sbornik, Gosgeoltekhizg, 3, 82–83.

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Palache, C., Berman, H., and Frondel, C., 1946. The System of Mineralogy, Vol. 1, 7th ed., John Wiley and Sons, Inc., New York .

Sokolova, E. P., 1959. Some new data on euxenite investigation, Vsesiu znoe mineralogicheskol obshchestno. Zapiski, 4, 408–418.

Von Stackelberg, M., and Chuboda, K., 1937. Dichte und Struktur des Zirkons II, Zeits, Krist., 97, 252–262.

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Professor C. Osborne Hutton, School of Mineral Sciences, Stanford University, Stanford, California.