613

SHORT COMMUNICATIONSBerlinite from Rwanda
THE occurrence of berlinite at Westans iron mine, near Nastim, Kristianstad, Sweden, forms the only previous record of A1PO4 in nature.
Independent examinations in England and Belgium of material from theBuranga pegmatite, in the Katumba region of Rwanda, show thatberlinite forms part of the exceptionally rich suite of phosphate minerals
developed in the pegmatite, a preliminary account of which has been
given by Bertossa (1961). The writers would like to thank Mr. A.
Bertossa and Dr. W. Krenning of the former Geological Survey of
Ruanda-Urundi for providing the specimens.
In one specimen, an elongated, whitish-coloured patch of berlinite
about 2 cm in thickness is bordered on one side by massive amblygonite
with disseminated lazulite and on the other by very fine-grained muscovite grading into a muscovite-apatite assemblage. At the contact of
the amblygonite and the berlinite, a micropegmatitic intergrowth of thetwo minerals is developed and isolated grains of amblygonite occur inthe berlinite. The berlinite forms anhedral grains, 0-5 to 6 mm across.
Twinning in the form of sub-parallel lamellae, 0-1-0-5 mm in width, isshown by many grains. In a second specimen, the berlinite occurs as ananhedral aggregate 2 cm across interspersed by bluish lazulite which isdeveloped chiefly at berlinite grain boundaries but also occurs as minuteveinlets. Individual grains of berlinite range from 0-1 to 3"0 mm acrossand sometimes show twinning.
The berlinite is uniaxial positive with refractive indices (determinedin sodium light) oJ 1"524 and E 1.532 (both •Determinations ofspecific gravity on small inclusion-free fragments using a torsion balancegave an average value of 2.66, compared with 2.62 calculated from thecell dimensions and an assumed cell-content of 3[ALP04].
The X-ray powder data and the lattice parameters have been derived
by Mr. D. Atkin from Cu-Ka photographs taken in a 114.6 mm diameter
Debye-Scherrer camera. The spacings and intensities are listed in table
I ; similar d-values were obtained independently by Mr. R. Vanderstappen. The powder lines were indexed by comparison with the diffractometer data for synthetic A1PO4 given on card 10-423 of the A.S.T.M.
X-ray Powder Data File. In checking the indexing by calculation,ssSHORT COMMUNICATIONS

614

TABLE I. X-ray powder data for berlinite from Rwanda; from photographs takenwith Cu-Ka radiation (~ 1.5418 ~) in a 114.6-ram diameter Debye-Scherrer camera;
intensities estimated visually by comparison with an intensity scaled, ~Ihkil

4.27
3.99

22
3logo
lOil

1.467

3-65
3.37
2.47
--

1100
7
--

0003
1052
1130
1121

--

2-3l

81054

2-25
2-14
1-991
1.831

57
3141.684--5-

-

--

--

--

--

1.551
--

10---

1132
2030
2022
1134
/ 20_24~ 1016
1125
2130

2131
2132
2033
2133

d, ~Ihkil

2t 11~_6( lO17

1"390
1"380

5
23030
/ 2134/ 2036
3032

1.303

1

1.265
1.236
1.209
--

2
12
--

-

1-197]

1'186-1.1602-1/ 21_~5( 1018/ 3034
[ 20372230
2136
2232
/ 3035[ 1128314022333142

additional reflections were found t h a t could contribute to three of thelines (1017, 1058, and 1158).
P r e l i m i n a r y values for the lattice parameters, derived from 4260 and
3360 (for a) and from 2.0.5.12 and 2.2.4.10 (for c), enabled reflections at
83.14 ~ and 86"66 ~ O to be indexed as 4264 31 and 4158 ~1 respectively.
These high-angle reflections in t u r n p e r m i t t e d a and c to be recalculated,t h o u g h the values were not in fact m a t e r i a l l y altered. The lattice parameters are listed below, t o g e t h e r with published determinations forsynthetic A1PO 4 and for berlinite from the t y p e locality.

ac

Synthetic A1PO4
Huttenlocher 1
A.S.T.M.
(1935, p. 516) card 10-423
4.94 ~
4.942 A]0.96 A
10.97 ~

Berlinite
Westanh mine
Buranga(Strunz, 1940)(this paper)
4.92/~
4.943 2_0.002
10.91/~
10.948•

Associated with the berlinite at Westan's mine are the phosphates
augelite, attacolite, and lazulite. Augelite and lazulite occur amongst
the v e r y wide v a r i e t y of phosphates recorded from the Buranga pegmarite and f r o m other pegmatites in the K a t u m b a region of R w a n d a(Altmann, 1961; Polinard, 1950; Van Tassel, 1961; Thoreau, 1954;
Thoreau and Bastien, 1954; Thoreau and Delhal, 1950; Thoreau and615

SHOI~T COMMUNICATIONS

Safiannikoff, 1957). Additional species identified b y the presentwriters f r o m the B u r a n g a p e g m a t i t e are phosphosiderite, purpurite,and fremontite.

Atomic Energy Division,
Geological Survey of Great Britain,London
Mus~e royal de l'Afrique eentrale,
Section de Gdologie,
Min~ralogie et PaHontologie, Tervuren

M . J . GALLAGHER2

J . F . GERARDS 2Ref~re~tce8
ALT~A~N (J.), 1961. Schweiz. Min. Petr. Mitt., vol. 41, p. 407 [M.A. 15-487].
BEttTOSSA(A.), 1961. Serv. g6ol. Ruanda-Urundi, Rapport annuel, vol. 1 (for 1960),
p. 23 [M.A. 16-63].
HVTTE~LOC~na (H. F.), 1935. Zeits. Krist., vol. 90, p. 508 [M.A. 6-183].
POLI•ARD (E.), 1950. IIIr Congr. Nat. Sci., Bruxelles, vol. 8, p. 18.
ST~V~z (H.), 1941. Zeits. Krist., vol. 103, p. 228 [M.A. 8 220].
T~OR~Av (J.), 1954. Bull. C1. Sei. Acad. l~oy. Belgique, set. 5, vol. 40, p. 231[M.A. 12-400].
- - and BASTIEN(G.), 1954. Bull. Acad. roy. Sci. Colon., Sect. Sci. nat., Brussels,
vol. 25, p. 1595 [M.A. 14-312].
- - - and DELItAL (J.), 1950. III e Congr. Nat. Sci., Bruxelles, vol. 8, p. 30.
- - - - and SAFIAN~IKOFF(A.), 1957. Bull. Cl. Sci. Acad. Roy. Belgique, ser. 5, vol.
43, p. 324 [M.A. 14-52].
VA?STASSEL (R.), 1961. Bull. Acad. roy. Sci. d'Outre-Mer, vol. 7 (3), p. 404.
1 Published values increased by 1 in 500 to convert kX to ~.
2 Published by permission of the Director of the Geological Survey of GreatBritain and of the Director of the Royal Museum of Central Africa, Tervuren.

Crystal structure of stokesite, CaSnSi~Og.2H20
STOKESITE was first described b y H u t c h i n s o n (1899, 1900) and later on
reinvestigated b y X - r a y and micro-analytical m e t h o d s b y G a y andRickson (1960). The present a u t h o r had an o p p o r t u n i t y to do X - r a y
crystallographic work (1961-62) at the D e p a r t m e n t of Mineralogy andP e t r o l o g y of the U n i v e r s i t y of Cambridge, England, during which hed e t e r m i n e d the crystal structure of stokesite. The specimen was kindly
supplied b y Dr. P. Gay.
The space group as d e t e r m i n e d by G a y and Rickson (ibid.) is Pnna
and the lengths of the axes are: a 14"465 ~, b 11"625 A, c 5.235 A. There
are four formulae units of stokesite in a unit cell. The i n t e n s i t y d a t a wascollected b y Weissenberg camera from the axial projections on (001),(010), and (100) using Mo-Ka-radiation. The trial structure wi~s concluded