GEOLOGICAL MAGAZINE 
NEW SERIES. DECADE Vik VO. INE 
7 No. IV.—APRIL, 1916. 
ORIGINAL ARTICLIEHS. 
J.—Two rarer OBsIDIANITES FROM THE RaFriEs Museum, SIncAPoRE, 
AND NOW IN THE GeonocicaAL Department, F.M.S. 
By J. B. ScRIvENOR, M.A., F.G.S. 
(PLATE VIL.) 
OME years ago I was asked to look through a collection of geological 
specimens in the Raffles Museum, Singapore, and found in a drawer 
two exceptionally large obsidianites. ‘They were not labelled, and 
nothing could be ascertained about their history, but an assistant in 
the Museum said he thought they might have come from Kelantan, 
a State on the east coast of the peninsula. The weights of the two 
obsidianites were 464 and 316°4 grams. ‘The former and larger of 
the two was entrusted to a local firm to cut in half, with the result 
seen in Pl. VII, Fig.1. The photograph, nevertheless, shows that 
there is a group of vesicles in the centre. The photographs, which are 
natural size, also show that there is nothing unusual about the surface 
of these specimens (Pl. VII, Fig. 2). 
. An analysis of a portion of the larger specimen has been carried out 
by Mr. C. Salter, Chemist in the Geological Department, F.M.S. 
In May, 1915, Dr. Mueller (Gruoz. Mae., 1915, pp. 206-11) described 
under the name of ‘ Tektite’ obsidianites from near Tutong, a dismal, 
erocodile-infested station in Borneo that I also have had the misfortune 
to visit, and gave an analysis by Dr. Hinden (op. cit., p. 209). The 
close agreement in composition of the Singapore specimen is note- 
worthy, and is shown in the following table (p. 146), together with 
some of the analyses quoted in a recent paper by Mr. C. G. Thorp 
(‘‘A Contribution tothe Study of Australites,” Journ. W. Australian Nat. 
Hist. Soc., vol. v, pp. 1-26, 1914), and others of obsidian from Iddings’ 
Igneous Rocks, and from a description by Dr. Prior of rocks from 
British Kast Africa (‘‘ A Contribution to the Petrology of British East 
_ Africa,’ Min. Mag., xiii, pp. 245, 247, 1903). The more important 
constituents only are given, and the analyses of ‘ Australites’ and 
‘Moldavites’ are selected from Mr. Thorp’s paper to show the 
extreme ranges of silica percentage. No. 12 is described by Dr. Prior 
as ‘‘phonolitic obsidian” ; No. 13 as ‘‘obsidian glassy soda-rhyolite”’. 
The range in silica percentage in obsidianites is shown by the 
analysis to be large. Dr. Mueller mentions the difference in the 
composition of obsidianites from that of obsidians. There is certainly 
a marked difference compared with the U.S.A. obsidians, but when 
one compares them with the East African rocks, which differ chiefly 
in the preponderance of Na,O over K, 0, and considers that a glass 
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