196 



E. A. STEPHENSON 



certain phases of the vein-forming process sulphide solutions must 

 be present. Though the solutions are undoubtedly very complex, 

 their efficiency as hydrothermal agents is very probably due to a 

 few components. The physical state of these solutions has been 

 recently shown by Tolman and Clark 1 to depend decidedly upon the 

 composition, at least at ordinary temperatures, and it may also 

 have some decided influence upon the character of the alteration. 

 In the following experiments the copper tubes were vigorously 

 attacked and chalcocite crystals lined the walls of the tubes 

 (Table IX). In No. 46 needles of the anisotropic crystals like those 



TABLE IX 



obtained in experiments Nos. 25 and 34 were formed, together with 

 well-formed analcite crystals. Very little of the original feldspar 

 remained. In No. 47 perfect analcite crystals appeared as icosite- 

 trahedra and as combinations of the cube and rhombic dodeca- 

 hedron. These vary in size from one-half to one millimeter in 

 diameter. The hornblende in experiment No. 48 was not attacked 

 and no pyrite could be identified in the product. No sulphur was 

 obtained by heating the mass in a closed tube. The results with 

 the feldspars are quantitatively greater than in any other experi- 

 ment; this was probably due to the fact that the hydrogen sulphide 

 is a weaker acid than is carbonic acid and the hydrolysis therefore 

 produces a more strongly alkaline solution. 



Group X: Aluminate solutions on feldspars and hornblende. — In 

 the previous experiments the loss of silica from the minerals resulted 

 in an apparent rise of the alumina content of the new minerals. 

 With the thought that possibly an increase in the concentration of 

 the alumina in the solutions might cause the solubility product for 



1 C. F. Tolman and J. D. Clark, Econ. Geo!., IX (1914), 559. 



