132 Cross and HUlebrand— Minerals in the basalt of 



F. Klocke * in a critical review of Eumpf's hypothesis (1. c.),. 

 advocated the theory of inner tension (Spanuungi in explana- 

 tion of the anomalous optical behavior of apophyllite. He also 

 showed that Rumpf's hypothesis could not correctly explain 

 phenomena in apophyllite much simpler than those above 

 described. 



In chemical composition this apophyllite is quite normal,. 

 the fresh substance yielding the following: 



Fe 2 3 



cn<> ;. 



K„0_. 



UJ>. 



100-691 

 for Fl 0-716 



The theoretical proportion 1:4:2 would be still nearer ap- 

 proached were it not for a probable slight loss of silica and excess 

 of water, scarcely to be avoided in analyses of silicates contain- 

 ing fluorine. The Fe,0 :; is undoubtedly owing to minute parti- 

 cles of limonite, which could not be completely removed. The 

 A1 2 3 is much higher than in most analyses, and the condition 

 in which it is present seems undeterminable. 



Much of the Table Mountain apophyllite has suffered altera- 

 tion to a snowy-white substance resembling that commonly 

 known as albine. Knop f has proved, for many cases at least. 

 latter substance is calcite. At Table Mountain, how- 

 ever, although the end product resembles albine, it is in reality 

 of totally different nature. 



Up to the present time it has been impossible to procure the 

 alteration product, sufficiently free from fresh or partially de- 

 composed apophyllite, to allow of its exact determination. 

 From analyses mad*', it is certain that Fl. the alkalies and Ca 

 decrease markedly, while the percentages of Si0 2 , A1 2 3 and 

 H 2 increase greatly. 



*F. Klocke. review of Rumpf's article. "TJeber den Krystallbau des Apophyl- 

 f In Blum, "Die I fritter Nachtrag," 1863, p. 41. 



