Differentiation in Silicate Liquids. 



179 



enough to prevent further crystallization. Occasionally, how- 

 ever, rims of amphibole formed about the olivine crystals. In 

 the mixtures with an excess of silica, from which pyroxene 

 first crystallizes, this tendency towards the formation of 

 amphibole during cooling was still more marked, indeed very 

 difficult to prevent in spite of the greater viscosity of the 



Fig. la. 







Fig. la. 

 25. 



Same as lowest section of fig. 1. Forsterite crystals in glass. 



liquid. This must be attributed to a greater power of the 

 pyroxene crystals to induce crystallization of amphibole. In 

 order to overcome this difficulty it was necessary to use very 

 much flattened crucibles which exposed a large cooling sur- 

 face. These were made by folding thin platinum foil into the 

 desired shape and had about the same depth (2*5 cm ) as had the 

 ordinary crucibles. 



