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



gray lava the vesicles of which are lined with a beautiful pink epidote on the top of 

 which is usually a layer of colourless, botryoidal prehnite. The epidote occurs in 

 groups of divergent crystals which are sometimes green at the one end and grade off 

 into pink at the other ; it frequently rests upon a layer of albite. 



The following analysis, made by Mr Radley, shows this variety to be a lime- 

 epidote, poor in iron, and owing its colour, doubtless, to the small amount of 

 manganese present : — 



Si0 2 



TiO, 



A1A 



Fe 2 3 



FeO 



MnO 



(CoNi)O 



CaO 



MgO 



K 2 



Na 2 



Li 2 



H 2 at 105° C. 



H 2 above 105° C. 



38-69 



•6405| 

 •0015/ 



•12 



28-54 



•2793| 

 •0435/ 



6-97 



•22 



•0030 



•29 



•0040 



nt. fd. 





23-78 



•4246 



•49 



•0121 



•03 





trace 



. . . 



trace 





•09 





•99 



•055 



Molecular Ratios. 



•6420 6-00 



•3228 



•4437 



3-01 



4-05 



•055 



•514 



100-21 



The above analysis gives the formula Ca 4 Al 6 Si 6 25 |H 2 0, in which the alumina is 

 partly replaced by ferric iron and the lime by ferrous iron. The mineral obviously 

 belongs to the somewhat rare series of epidotes poor in ferric iron referred to by 

 Dr H. H. Thomas in his description * of an epidote from Inverness-shire ; it is also 

 peculiar in having only half the normal percentage of water. Owing to the fibrous 

 and poorly crystallised nature of the material an accurate determination of the 

 optical characters was impossible ; but, by means of a solution of methylene iodide 

 and benzene, the mean refractive index was found to be 1*720, which accords well 

 with the values given by Dr Thomas. 



Prehnite is a fairly common mineral in the vesicles, and occurs in the usual 

 botryoidal form ; sometimes it forms a dense white massive layer which is occasionally 

 spotted with little yellowish or reddish masses of garnet. Typically it occurs in 

 globular growths underlying the scolecite and seated upon epidote or albite. It is 

 most plentiful at the locality previously noted in connection with the pink epidote. 

 There, the geodes found in the screes are usually dull and weathered on the surface, 

 but when broken open show beautiful rosettes of epidote projecting into massive 

 white prehnite. In cavities in the latter mineral there occurs occasionally a pale 



* H. H. Tiioma.s, " On an Epidote from Inverness-shire," Minuralogical Magazine, vol. xiv, p. 109. 



