Vol.8 N o . 4 CHINESE JOURNAL OF GEOCHEMISTRY 1989

A New Mineral Ximengite

Shi Jiaxin ( ~ I ~ ) ( Bureau of Geology and Mineral Resources, Yunnan Province, Kunmin#)

The new mineral ximengite occurs in a tin deposit at Ximeng County (about 420km southwest of Kunming) , Yunnan Province. Its associated minerals are: waylandi te , monazi te , and other two unnamed bismuthic minerals : Bi-phosphate and Bi-sulfate (tentatively named hydroxylphosphabismite Bi2PO4(OH) 3(? ) , and hydroxyls'ulfabismite Bi2SO4(OH)4(? ) ) ( P h o t o s A-F) . They are all contained in the cassiterite-tourmaline-quartzitized migmatit ic rocks.

Appearance and Physical Properties

Earthy aggregates of microcrystals (0.001 to 0.1 m m in diameter) . Colour �9 colourless with a white streak ; lustre : oily to vitreous ; transparent to translucent, V H N = 279 - - 283 kg /cm 2, brittle. Cleavage : not observed ; Density : not meas- ured because of its small grain size. Density ( c a l c . ) - 5. 534 g / cm 3 (dry crystals). Zeolitic water is assumed to be 0.13 H20 for synthetic ximengite (see chemical data) with De= 5. 576 g /cm 3

Optical Properties

Grey with colourless internal reflections. Fluorescent effect, yellowish-green un- der the electron microscope;refractive index : No> 1.77 (uniaxial positive for synthetic ximengite). Reflectance values were measured by means of a n MPV-I I microphotometer ( Table 1). Determination condition : ,h, = 5.6 - - 8 . 0 ; V= 8 3 7 - - 1297; background value , 0.1 ; s tandard reflector, SiC ; immersion oil N= 1. 5180 ; ocular 10x ; objective lens 20x ; aperture 10 • 10/z m . Colour indices were calculated by Wang Daishi ( T a b l e 2) . R v.s ( 4 5 ~ : 10. 6% () , d .. . . ant 472nm , Pe 0.045) in air ; 1.8% (2 d 512 n m , Pe 0.015) in o]1.

Table I . The wavelength (nm)-reflecfing power (R) data for ximengite

Sample Medium N o .

A i r F7

Oil

Air

F 6 - 4 Oil

Sample Medium NO, F7 Air

oil

Air F 6 - 4

Oil

Analyst : Jia Hong .

Orien- tation R 45 ~ R 4~ ~ R~' Rp ' R8' Rp'

Orien- tation R45 o

R 4~ Rg ' Rp' Rg'

Rp'

400

11.8 1.9

t l .2 10.5

1.6 1.5

560

10.7" 1.8

10.2 J

9.6 1.5

1.3

420

11.5 1.9

11.2 10.5

1.6 1.4

580

10.6 1.9

10.3 9.8 1.5 1.4

440 460 470 480 500 520 540 546

11.5 11.9 11.9 10.9 10.7 10.6 10.6 10.6 1.9 1.8 1.8 1.8 1.7 1.7 1.8 1.9

11.2 10.6 10.8 10.8 10.7 10.6 10.5 10.3 10.4 10.1 10.1 10.1 9.9 9.9 9.8 9.6

1.6 1.5 1.7 1.7 1.6 1.5 1.5 1.5 1.5 1.4 1.6 1.5 1.4 1.4 1.4 1.4

589 600 620 640 660 680 700

10.6 10.3 10.1 10.1 10.1 10.0 10.0 1.8 1.9 1.9 1.7 1.8 1.8 1.8

10.4 10.4 I0.1 10.2 10.2 10.2 10.2 9.9 9.6 - 9.6 9.6 9.6 9.'~ 9,7 1.6 1.6 1.5 1.6 1.5 1.6 1.4

1.5 1.5 1.4 1.5 1.4 1.3 1.3

386 CHINESE JOURNAL OF GEOCHEMISTRY Vol.8

Table 2 . Coiour index of reflcting power of xhnengite

Sample. Medium No.

Air F7

O~

Air

F 6 - 4

Oil

Orien- tation

R 45

R45 ,o

Rg '

Rp'

Rg,

Rp'

X Y Z Rws 2d Pe

0.3010 0.3055 0.3935 10.6 472 0.045

0.3118 0.3138 0.3744 1.8 512 0,015

0.3046 0.3103 0,3851 10.4 475 0.028

0.3053 0.3103 0.3844 9.8 471 0.024

0,3075 0.3104 0.3821 1.5 566 0.020

0.3089 0.3095 0.38t6 1.4 558 0.032

Chemical D a t a

Ximengite was analyzed for chemical composition on a JSM-35CF scanning elec- tron microscope and an EDAX PV 9100 energy spectrometer using the following standards : bismuthite (Bi) and apatite ( P ) . The analytical results are : Bi203 76.34 ; P205 22.92 ; total 99.26 wt . % (Table 3). If zeolitic water present in synthetic ximengite (0.76 wt .%) is added, the total is 100.02 wt . % . The empiri- cal formula (based on 4 oxygen ions) is : Bi 10t P o.9904.00 (zeOlitic water molecule = 0.13 H20) . The simplified formula is BiPO 4.

The DG-DTA and infrared absorption spectral analyses of synthetic ximengite (hexagonal BiPO 4) (Figs. 1 - - 2) showed that hexagonal BiPO 4 normally contains zeolitic water and adsorbed water , but no crystalline water and hydroxyl group. When heating the synthetic ximengite at 2 0 - 1100 ~C , weight loss occurs mainly at 35 - - 175 ~ , and an endothermic peak appears at 112 ~ The contents of adsorbed water and zeolitic water correspond to a weight loss of 3.87%from 20 to 217 ~ The adsorbed water corresponds to a weight loss of 3.11 wt . % from 20 - - 100 ~ , while the zeolitic water corresponds to a weight loss of 0.76% from 109 to 217 ~ As revealed by X-ray diffraction analyses, no change has taken place in crystal structure in spite of weight loss. The hexagonal BiPO 4 is converted to the monoclinic BiPO 4 with minor monazite-type BiPO 4 associated at 9 0 0 - - 1100 ~ (Table 4 ).

Qualitative analysis of ximengite showed that it was composed essentially of P

and Bi with minor other elements.

Table 3. Quantitative amiyses of ximengite

Line of element

P K Bi M O total

Wt .%

10.00 68.48 20.78 99.26

at. %

16.56 16.81 66.63

100.00

' O ' %

22.92 76.34

99.26

% S . e .

0.85 0.52

Analysts : Yang Linchang, Meng Xing and the author.

No.4 C H I N E S E J O U R N A L O F G E O C H E M I S T R Y 387

22

~ ~ TG

200 900 11 O0

Fig. 1. TG-DTA curves for the synthetic ximengite. (Analysts : Zhang Shanghua and Li Jianmin)

~ C

3440

3430

1605 U 59 5

163o \ / U537 600

1015

Fig. 2. Infrared absorption spectra of the synthetic ximengite. (Analyst : Deng Yaomin)

A. Not heated; B. heated to 217 E for lhr ; C and D .

Table 4 . X-ray powder diffraction data .for mon~ink BiPOA File (JCPDS) 16- 682 Synthetic ximengite heated to 1100 ~E

d ( A ) I / / o h k

4.85 20 1 4.66 25 0

3.99 35 1 3.90 45 0 3.56 100 1 3.54 95 0

3.19

2.918 2.853 2.826

2.517

12

60 8 6

45

0 0 4.852 0 I 4.677

A 4.165 A 4.087

1 0 4.002 1 1 3.903 0 - I 3.570 2 0 3.534

A 3.282 0 1 3.197

A 3.071 1 1 2.913 2 1 2.860 2 ! 2.82l

A 2.596 2 - 1 2.511

reference KBr.

16 1.559 5 28 1,544 6 10 1.533 2 5 1.530 2

50 1,512 0 44 1.499 1 90 1.479 1

100 1.471 1 10 1.457 1 9 1.446 1

19 1.409 5 71 1.365 2 18 1.357 3 5 1.353 2 3 1.331 3

31 1.322 2

1/I o d (A) 1/Io

388 C H I N E S E J O U R N A L O F G E O C H E M I S T R Y V o l . 8

cont inued

File (JCPDS) 16- 682 Synthetic ximengite heated to 1100

d(A ) I/Io h k I d (A) l / I o d(A) I/Io

2.437 16 2 0. 0 2.368 4 1 2 ~l 2.342 30 0 0 2 2.300 40 2 1 0 2.263 18 2 0 - 1 2.225 35 0 1 2 2.210 6 1 0 - 2 2.155 16 2 1 - 1 2.116 25 1 3 0 2.107 35 1 1 - 2 2.068 .20 2 0 1 2.026 20 1 0 2 2.004 2 2 2 0 1.984 4 2 1 1 1.952 12 0 2 2 1.899 30 1 3 1 1.870 6 1 2 - 2

1.786 20 2 0 - 2 1.769 10 0 4 0 1.759 10 1 2 2 1.733 6 2 1 - 2

1.694 14 2 3 0 1.658 14 1 4 0 1.631 4 2 3 - 1 1.617 6 3 0 0 1.608 12 1 3 - 2 1.598 12 2 0 2 1.585 14 3 0 - 1

Plus 10 lines to 1.446

A 2.443 2 1.311 2.427 4 1.292 2.369 1 1.256 2.338 8 1.247 2.294 33 1.228 2.256 5 1.221

1.207 2.212 12 1.190 2.148 7 1.185 2.120 21 1.175 2.103 27 1.145 2.063 12 1.118 2.021 7 1.116

1.104 1.960 3 1.055 1.949 7 1.896 25 1.870 3

A 1.866 3 1.782 17 1.766 7 1.754 8 1.734 4

A 1.728 5 1.689 10 1.659 7 1.628 3 1.610 5 1.609 5 1.593 6 1.583 6

A Due to monazite-type BiPO4 (see JCPDS card 15-767).

Crystallography

Single-crystal X-ray studies could not be done because single ximengite crystals are too tiny to be separated from the aggregates. X-ray Debey-Sherres powder photo- graphs (Jin Zeng) and X-ray powder diffraction data for ximengite and synthetic ximengite were obtained by means of a Geigerflex D/Max-3A diffraction sys- tem (Table 5). The powder pattern was indexed by analogy with that of the synthet- ic material t J J. Unit cell data and d c values for ximengite were calculated. Essential parameters are. hexagonal, P31 21, a = 6 . 9 8 6 0 ( 1 6 ) , c = 6 . 4 7 5 3 (28) A ,

O

V= 273. 68 A 3 , Z = 3. Morphology- the c ' a ratio calculated from the unit cell parameters is 0.9269.

No .4 C H I N E S E J O U R N A L O F G E O C H E M I S T R Y 389

Table 5 . X-ray powder diffraction data for ~dmengite and synthetic hexagonal bismuth phosphate

Ximengite d ( ~ ) I / /o

6.052 73 4.4198 91 3.4930 88 3.0724 34 3.0244 100 2.8537 65 2.3738 8 2.2850 6 2.2090 3 2.1573 47 2.0304 12 2.0197 2 1.9268 16 1.8683 45 1.8368 10 1.7572 10 1.7474 48 1.7114 19 1.6752 10 1.6216 13 1.5720 1.5639 16 1.5387 3 1.5139 2 1.4872 4 1.468 3 1.370 3 1.357 4 1.321 4 1.294 3 1.274 4' 1.265 3 1.261 4 1.238 4 1.222 5 1.188 1.166 1.145 1.142 1.131 1.122 1.085 1.069 1.053

m

Synthetic BiPO4 (low form) File (JCPDS) 15 - 766 This text

d(~) I/Io h k l

6.06 65 100 4.421 100 101 3.494 45 110 3.073 45 111 3.025 95 200 2.854 80 102 2.375 30 112 2.286 12 210 2.211 6 202 2.156 60 211 2.032 6 103 2.016 4 300 1.925 20 301 1.867 50 212 1.837 6 113 1.7571 25 203 1.7452 36 220 1.7115 20 302 1.6774 12 310 1.6239 12 311 1.5693 6 213 1.5644 12 104 1.5368 6 222 1.5118 6 400 1.4892 12 312 1.4687 10 114 1.3698 4 402 1.3563 14 321 1.3206 16 214

1.2750 10 322 1.2667 6 105 1.2624 8 304 1.2384 2 403 1.2217 6 412 1.1885 6 501 1.1639 8 330 1.1450 4 331 1.1425 4 420 1.1328 6 " 502

413 510

1.0709 422 324

Heated to 217

6.046 4.419 3.490 3.072 3.022 2.853 2.372 2.284 2.209 2.154 2.032 2.014 1.924 1.867 1.835 1.7564 1.7449 1.7106 1.6768 1.6231 1.5693 1.5637 1.5365 1.5115 1.4850 1.4682 1.3695 1.3564 1.3201 1.2927 1.2749 1.2658 1.2618 1.2380 1.2215 1.1887 1.1637

1.1424 1.1325 1.1256 1.0858 1.0708 1.0530

54 30 30 18

100 24

9 6 1

30 1 1

11 20

1 6

"10

9 7 0 0 1

6.044 4.417 3.488 3.071 3.021 2.852 2.372 2.284 2.208 2.154 2.031 2.014 1.924 1.866 1.835 1.7560 1.7444 1.7103 1.6766 1.6230 1.5690 1.5633 1.5358

3 1.5110 2 1.4887 2 1.4682 1 1.3691 6 1.3563 5 1.3200 2_ 1.2925 4 1.2746 0 1.2662 1 1.2619 1 1.2379 2 1.2214 1 1.1884 2 1.1637

1.1448 1 1.1422 1 1.1325 I 1.1254 2 1.0856 0 1.0706 1 1.0530

I / / 0

50 39 30 19

100 26 11 7 I

35 1 1

13 23

1 7 9 9 9 7 0 2 1 5 6 2 1 7 5 3 5 0 2 1 3 1 2 0 1 2 1 2 0 1

The mineral is named after the area where it was found (Ximeng). material is preserved at the Geological M useum, Bureau of Geology and sources, Kunming, Yunnan Province.

The typical Mineral Re-

390 C H I N E S E J O U R N A L O F G E O C H E M I S T R Y Vol .8

Discussion

Ximengite is similar to rhabdophane on the basis of X-ray diffraction and TG da- ta . But their space groups might be different : hexagonal BiPO4-P3j21 I 21, and hexagonal CEPO4-C622.

As revealed by X-ray diffraction, TG-DTA and infrared absorption spectral ana- lyses of the synthetic ximengite, it contains adsorbed water and zeolitic water, but no crystalline water and hydroxyl group. The crystal structure has not been affected by the losses of adsorbed water and zeolitic water , as indicated by X-ray diffraction studies of synthetic hexagonal CePO 4 by Mooney (1950) t 31 He stated : " It is rea- sonable to suppose that the crystals ordinarily contain zeolitic water , but there is no real evidence to prove whether or not the presence of water is necessary condition for the stability of the hexagonal-type structure " However, no analytical data for the water in rhabdophane had been reported in the literature.

Whether or not ximengite and rhabdophane belong to the same mineral group is uncertain.

References

[ 1 ] Swanson et a l . , National Bureau of Standards (U.S.) Monograph 25 sect., 3 (1964), [ 2 ] Mooney-Slater ,Z . Krist. 117 (1962), 371 - - 385. [ 3 l Mooney, R .C. L . , Acta Cryst. 3(1950), 337-- 340.

13.

No .4 C H I N E S E J O U R N A L O F G E O C H E M I S T R Y 391

Photos A - F : SEM photographs of ximengite and its associated minerals. 1. Bismuthinite ; 2. ximengite ; 3. unnamed mineral hydroxylphosphablsmite ; 4 . unnamed mineral hydroxylsulfab/smite ; 5. waylandite ; 6 . monzaite ; 7. tourmaline ; 8. cavity.