8 MR W. F. P. M'LINTOCK ON THE ZEOLITES AND ASSOCIATED MINERALS 



The following analysis was made by Mr Radley, and shows the mineral to be 

 a typical lime-alumina garnet : — 



Si0 2 . 



37-66 



Ti0 2 . 



•12 



A1A . 



21-84 



Fe 2 3 . 



4-07 



FeO . 



•34 



MnO . 



•53 



(CoNi)O 



. nt. fd. 



CaO . 



33-06 



MgO . 



•45 



K 2 . 



•75 



Na 2 . 



1-17 



Li 2 . 



. nt. fd. 



H 2 at 105° C. 



nt. fd. 



H 2 above 105° C. 



•20 



Sp. g. = 3-61 



100-19 



at 7° C. 



Albite is not infrequently found in the vesicles in association with the minerals 

 already described. It rarely shows crystal form and occurs usually as a massive 

 layer of variable thickness underlying scolecite or prehnite. When scolecite is 

 present the layer of albite is separated from it by an irregular layer of epidote, 

 whilst when prehnite overlies the felspar a zone of garnet occasionally separates the two. 

 Vesicles also occur lined, with albite upon which a layer of green epidote is seated, 

 and albite-filled veins are of frequent occurrence in the lavas. The layer underlying 

 the albite occasionally presents unusual features. In a few specimens it consists of 

 white massive albite speared by long black fibrous crystals, measuring up to -5 cm. 

 in length and consisting of augite which, under the microscope, has the purple tint 

 typical of the Tertiary basaltic lavas. These crystals occasionally wander into the 

 albite of the vesicle proper, but the point will be more fully discussed when the 

 microscopic characters of the vesicle-minerals come under consideration. 



When crushed and examined under the microscope the albite is easily identified 

 by the usual twinning, the symmetrical extinction angles on twin-lamellae, and by 

 its mean refractive index, which, tested in oil, is approximately l - 534 ; it is rarely 

 clear and transparent, being usually filled with inclusions. 



The lavas underlying the vesicular zone under consideration are much more 

 compact and are characterised by much smaller amygdales which are filled with 

 dense white or pink massive albite associated with epidote. 



Calcite. — From the mineral association so far described, one might have expected 



