108 wherry: phosphate and silicate minerals 



The nature of the white lamellar mineral can not be definitely 

 made out from the data at hand. Of the constituents found in 

 the second analysis, all of the P 2 5 and part of the A1 2 3 and H 2 

 are undoubtedly due to the admixed green material; if this 

 amounted to one third of the whole, then the approximate com- 

 position of the white mineral would be CaO 17, A1 2 3 17, Si0 2 47 

 and H 2 19, corresponding roughly to the ratios of these four 

 constituents, respectively, 2 : 1 : 5 : 7. No amorphous mineral 

 of this composition appears to be on record, although the crystal- 

 line zeolite laubanite differs only in having slightly less water. 

 However, the mean index of laubanite, as determined by Dr. 

 Larsen 8 is 1.475, while that of the present mineral is higher, vary- 

 ing from 1.53 to 1.54, so the two must be entirely distinct. It 

 may be noted that the mineral fuses with intumescence before 

 the blowpipe, so that it evidently belongs to the zeolite group, 

 but under the circumstances it would be unsafe to assign a name 

 to it. 



Although in many aluminium phosphates siliceous impurities 

 have been found to be present, no definite intergrowth relations 

 have heretofore been reported to exist between the two. The 

 structure here shown is not difficult to explain, however, when 

 the colloidal character of the materials is considered. The lamel- 

 lae have the aspect of forms produced by rhythmic precipitation 

 in gels, such as obtained in many of the experiments described 

 by Liesegang 9 and others. In this case if, while the phosphate 

 gel was still soft, a solution containing calcium and silica flowed 

 over it, reaction might readily have occurred, with removal of 

 part of the phosphoric acid and formation of a calcium aluminium 

 silicate with the liberated alumina. 



The material studied is regarded, then, as a colloidal vashegyite 

 traversed by rhythmically precipitated laminae of a calcium 

 aluminium silicate of probably zeolitic nature. 



8 Private communication. 



9 Geologische Diffusionen, Dresden and Leipzig, 1913. 



