Canadian Mineralogist
Vol. 27, pp. 533-534 (1989)
THE GLADSTONE-DALE CONSTANT k(U03) FOR URANYL PHOSPHATES
AND ARSENATES
PAVL PIRET
Laboratoire de Chimie physique et de Cristallographie, Universite Catholique de Louvain, 1, place Louis Pasteur,
B-1348 Louvain-Ia-Neuve, Belgique
MICHEL DELIENS
Section de Mineralogie et de Petrographie, lnstitut royal des Sciences naturelles de Belgique,
29, rue Vautier, B-1040 Bruxelles, Belgique
ABSTRACT
The best value for the Gladstone-Dale
constant k(U03)
for uranyl phosphates and arsenates is approximately
0.134;
this value was calculated from the data for 12 well-defined
compounds.
Keywords: Gladstone-Dale
arsenates,
compatibility.
relationship,
V03,
phosphates,
SOMMAIRE
Pour les phosphates
et arseniates d'uranyle,
la meilleure
valeur de la constante k(U03) de Gladstone-Dale
est aux
alentours de 0.134; cette valeur a ete calculee it partir des
donnees provenant
de 12 composes bien definis.
Mots-ctes: relation de Gladstone-Dale,
arseniates, compatibilite.
V03, phosphates,
In the definition of new minerals, the value of the
"compatibility index" (Mandarino 1981) represents
an important criterion for checking the internal consistency of some of the data. The method is based
upon a comparison of two quantities: Kp and Kc.
The first is calculated
from physical data:
Kp = (n-1)/D, wheren is the meanindexof refraction and D is the density. The second is calculated
from the chemical composition: Kc = EkiPj, where
Pi represents the weight fraction of a constituent,
and ki, the corresponding Gladstone-Dale constant.
The k values were calculated mainly by Larsen
(1921) and by Mandarino (1976, 1981) and may vary
with the kind of compound (silicate, phosphate, sulfate, etc.). In the case of uranyl compounds, the
value of the constant k for V03 of Mandarino
(0.118) is very different from that of Larsen (0.134).
In Table 1, we have selected 12 compounds for
which the indices of refraction, the chemical compositions and crystal structures are particularly well
. defmed. In each case, we have verified that the meas-
ured density is near the calculated density Dx and
533
used the latter (which is generally more precise) in
the calculation of k(U03):
(n-1
k(U°3)
= Dx - EkiPj)/p(V03)
where kj are the values proposed by Mandarino
(1981). Of course, EkiPj does not include V03. An
examination of Table 1 ~hows that Larsen's constant is better for uranyl phosphates and arsenates.
As the mean value of k(U03)' 0.133, is not significantly different from Larsen's value (0.134), it is suggested that Larsen's value be applied.
The mean values of the twelve compatibility
indices using 0.134 for k(U03) is 0.026 (in the
"excellent" category), whereas it is only 0.061 (in
the "fair" category) for k(U03) = 0.118.
TABLE 1. VALUES OF k(U03) CALCULATEO FROM OENSITY Ox. MEAN 1NOEX
OF REFRACTION
CHEMICAL COMPOSITION. . ANO
. OTHER GLAOSTONE-OALE
CONSTANTS k*
n.
HUgel ite
3UO,. 2PbO.As,O, .5H,O
Oumontite
3UO, .2PbO.P,O, .5H,O
Phurca li te
3UO,. 2CaO. P,O, .6H,O
A1thupite
7UO,.0 .5Al,0,. ThO, .2P,O,. 17 .5H,O
Upalite
3UO, .0.5Al,0,.
P,O,. 7.5H,O
Metatorberni
te
2UO,. CuO. P,O, .8H,O
Abernathyite
2UO,. K,O.As,O, .6H,O
Syntheti c compound
3UO,.P,O,.5H,O
Phura 1umite
3UO, .A1,O, .P,O,. 13H,O
Syntheti c compound
4UO, .K,O. 2As,O,. 15H,O
Syntheti c compound
2UO,. (NH. ),O.As,O, .6H,O
Threadgo 1di te
4UO, .Al,O,. 2P,O,. 17H,O
Ox
n
k(UO,)
5.80
1.907
0.148
a
5.66
1.87
0.140
b,c
4.26
1. 723
0.141
d
3.98
1. 649
0.131
e
3.94
1. 664
0.137
f,g
3.70
1. 624
0.123
h.,i
3.57
1. 595
0.132
if
3.53
1.577
0.141
3.52
1.613
0.123
(1,1
3.52
1. 598
0.131
if
3.43
1.608
0.124
if
3.32
1. 581
0.126
m
Mean
0.133
Refer.
References:
a Walenta (1979), b Piret & Piret-Meunier
(1988), a
Thoreau et ai. (1958), d Oeliens & Piret (1978), e Piret & Oeliens
(1987), f Piret & Oeclercq (1983), g Oeliens & Piret (1979a), h
Ross et ai. (1964), i Hallimond (1920), if Ross & Evans (1964). k
Sidorenko et ai. (1975), i Piret et ai. (1979), m Deliens & Piret
(1979b).
Taken from Mandarino (1976).
The mean value of k(U03)
is 0.133. *
534
THE CANADIAN
MINERALOGIST
_
ACKNOWLEDGEMENTS
We thank Dr. J .A. Mandarino, who concurs with
the k value proposed for uranyl phosphates and
arsenates, and who suggested that we publish this
note.
_
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_,
_
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J.P. (1979):Structureof
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Received November 21, 1988, revised manuscript
accepted December 20, 1988.