G. T. TRIOR. 
112 
of Kilimandjaro described by Finckli. * The leucites show a refraction markedly 
less than that of Canada balsam. In most of the small crystals the central inclusion 
of base occupies the greater part ; in many also the outer edge is invaded by the 
minute felspar-laths which generally form a fringe round the crystal. That the leucitic 
material in these rocks is only in small amount is indicated by the result of the bulk- 
analysis (see p. 113), and more especially by the partial analysis of the part soluble 
in nitric acid, the result of which is as follows, under I : — 
(Nephelino.) 
Si0 2 
= 43 • 12 
43-74 
Al,O a , Fe.,0, 
=- 33-32 
34-48 
CaO 
= 2-G3 
— 
Na 2 0 
= 14-96 
1G-G2 
K.,0 
= 3-73 
4-55 
Cl 
-- 0-70 
— 
H 2 0 etc. (diff.) 
= (1-54) 
0-8G 
100-00 
100-25 
The rock-powder gelatinised readily with acids, and as much as 25% was decom- . 
posed by half an hour’s digestion with dilute (1:5) nitric acid. Under II is given, for 
comparison, the result of an analysis by Clarke of a nepkeliue from Litchfield, Maine. 
The result of the above analysis suggests, therefore, that the soluble portion of the 
rock consists mainly of nepheline. 
An attempt was made to separate the leucites in the rock-powder by means of 
heavy liquids, but the grains which floated in a liquid in which moonstone sank and 
leucite floated were in very small amount, and of these only a few remained dark 
between crossed nicols. 
The anortkoclase-phenocrysts in all these rocks have the characteristic lozenge- 
shape determined by the development of the faces M (llO), m(110), and y (201). 
They almost invariably show minute twin-striations, occasionally in two rectangular 
directions according to the albite- and pericline-laws. Like the similar phenocrysts in 
the kenytes of Mount Kenya, they contain numerous inclusions of glassy base, and also 
occasionally inclusions of olivine, augite, apatite, and magnetite or ilmenite. On this 
account no chemical analysis was attempted. In physical characters they agree 
perfectly with the anorthoclases of Pantelleria and Kilimandjaro. The specific gravity 
is 2-G2. Cleavage-flakes parallel to b (010) show a positive bisectrix, slightly inclined, 
and give an extinction-angle with the trace of c(00l) of about G°, while cleavage-flakes 
parallel to c (001) have extinctions of about 1°. The refraction was about the same as 
that of clove-oil (1-538). Wolff (quoted by Finckh) found the value of y na for the 
anorthoclase of Kilimandjaro to be 1 • 537G. 
Nepheline was not found as phenocrysts in these rocks, neither could it be with 
certainty detected in the base, but that it is present is indicated by the results of the 
bulk-analysis. 
* Finckli, l.c., p. 382. 
