414 



Scientific Proceedings, Royal Dublin Society. 



This affords the formula — 



4-3 (Ka 2 (AL)Si 3 O 10 + 2H 2 0) 

 1 (Ca (Al 2 )Si 3 O 10 + 3H 2 0) 



or, according to Ranimelsberg — 



(9 Na 2 (Al 2 )Si 3 O I0 + 2H 2 0) 

 (2 Ca (Al 2 )Si 3 O 10 + 3H 2 0) 



But the amount of H 2 required for this formula does not 

 agree with that found upon analysis. Hauer, 1 who has investi- 

 gated several of the Scottish lime-bearing natrolites, gives an 

 analysis of a zeolite from Campsie Hills, which we can compare 

 with that from Kenbane Head. The quantity of H 2 found is 

 very nearly identical with that demanded by the empirical for- 

 mula. 



It should be especially brought under notice at this juncture 

 that, as scolezite contains 3H 2 0, whilst natrolite has only two, 

 it is very necessary to an accurate analysis of a mineral repre- 

 senting an isomorphous mixture of these two substances that 

 the H 2 found be in agreement with the calculated formula. 



It is manifest from the foregoing that the zeolite from Kenbane 

 Head must be regarded as no true natrolite. It is rather an iso- 

 morphous mixture of natrolite and scolezite, such as that described 

 under the name of galactite. The amount of lime, however small 

 it may appear, cannot but be considered as forming an integral 

 portion of the mineral. As the powder does not effervesce with 

 acids, it cannot be ascribed to the presence of foreign calcareous 

 matter ; optically, also, there is no evidence to show that the 

 mineral is merely natrolite, with an accidental admixture of scole- 

 zite. Neither does it appear that the lime arises from the presence 



1 Wien. Ak. Ber. : 1854. 



