138 Reports and Proceedings—Mineralogical Society. 
heat caused by the atmospheric oxidation of pyrites, a number of 
uncommon mineral species have been formed, of which five have been 
recognized, viz. native sulphur, sal-ammoniac, tschermigite, mascag- 
nite, and a possibly new species, aluminium sulphate.—Professor W. J. 
Lewis: A Crystal-holder for measuring large specimens. For this 
purpose a clamp of convenient form and with various adjustments 
has been designed and made by Mr. Pye.—Mr. T. Crook: Some 
observations on Pleochroism. The phenomena of pleochroism dis- 
played by plates of coloured minerals when examined in ordinary light 
were treated in a general way for both parallel and convergent rays, 
and the factors upon which they depend were discussed.—Mr. L. J. 
Spencer: Notes on the Weight of the ‘Cullinan’ Diamond, and on 
the Value of the Carat-weight. Varying statements of the weight of 
the ‘Cullinan’ diamond, in its original, uncut form have been 
published, but from a comparison of the carat-weights against which 
it was weighed in 1905 it is concluded that the correct weight was 
621:2 grams, or 30252 English carats of about 205°304 milligrams (as 
defined by the Standards Department of the Board of Trade in 1889). 
Other values are, however, given for the English carat and for the 
carat in other countries, and the average value has decreased on the 
whole in course of time. The carat-weight had its origin in the use 
as weights of seeds of Ceratonia siliqua, which weigh approximately 
a carat. The existing confusion would be obviated by the general 
adoption of the metric carat of 200 milligrams (one-fifth of a gram) 
recently recommended by the International Committee of Weights 
and Measures (JVature, 1908, vol. 1xxii, p. 611).—Dr. G. T. Prior: 
On a Basalt from Rathjordan, Co. Limerick. Specimens of basalt 
from Rathjordan in the Allport Collection in the British Museum show 
in thin slices under the microscope round sections of isotropic material 
containing central and marginal inclusions, and thus resembling small 
leucites. The rock is very similar, mineralogically and chemically, to 
leucite-basalts from Bohemia, but contains only a small fractional 
percentage of potash. This fact, combined with observations of the 
refractive indices, leads to the conclusion that the isotropic material 
is mainly analcite and not leucite.—Dr. G. F. H. Smith and Dr. G. T. 
Prior: On a Fluo-arsenate from the Indian manganese deposits. 
A erystallographical and chemical examination made of the green 
arsenate from Kajlidongri, Jhabua State, mentioned in Mr. Fermor’s 
monograph on the manganese-ore deposits of India (Rec. Geol. Surv. 
India, 1908), led to the following results :—Composition (Mg F) Ca 
AsO, Specific gravity, 3°768. Hardness, 33. Colour, apple- to 
brownish - green. Monoclinic: a: b:c = 0°7485:1: 0°8453 : B= 
120° 50’. Forms present (010), (110), (111), (181), (811), (112), 
(152). Good cleavage parallel to (101), and partmgs parallel to 
(110), (102), (881). Twin plane (100). Refractive indices, 1°640, 
1660, 1°666. Acute bisectrix nearly perpendicular to (101), and 
axial plane at right angles to the plane of symmetry, but no horizontal 
dispersion was noticed; 2E= 105° approximately, with negative 
birefringence. The mineral is probably identical with tilasite, which 
was first described by Sjégren in 1905, from the manganese deposits 
of Langban, Sweden.—Mr. H. E. Clarke and Professor H. L. Bowman : 
