879 



of the prepai'ation gives already immediately (lie same impression. 

 Most chai'actei'istic', is the syslem of eleavage-direclions which seem 

 to cover the plates as with a fine net-work of lines in three direc- 

 tions, arranged [)erpendicnlar]y lo each oilier in space. The lioundaries 

 of the tables are often I'ectangidai-; they show normal extinction. 

 The refractive indices are: 1.545 |)arallel lo the axis of elongation 

 of the crystals, and 1.525 poi'|)endicnlarly to it. The birefi'inüence 

 is of positive character and about : 0.020. 



Often twins or very complicated iniergrowths occnr. 



e. 79.67„ SiO, [= 66.0 Mol. Proc.j. 



The preparation is again fairly homogeneous. Oidy some line 

 needles are found locally on the table-shaped crystals, probably 

 representing the metasilicate. This fact would prove, that the bisilicate 

 will dissociate on melting. The birefringence is positive and about: 

 0.020; the refractive indices are fonnd to be about : 1 .545 and 1.530. 

 Many parallel intergrowths, and poly synthetical twins seem to be 

 present; the tine lines, indicating the system of cleavage-directions, 

 are here most typical. Locally the preparation shows a little (piantily 

 of glass. 



ƒ. 75.7"/,, SiO, (= 60.7 iMol. Proc). 



riiis preparation is inliomo- 

 geucous; longshaped needles, 

 with II -=z 1.585 and uoruial 

 exiiiicliou are intei'growi» wiili 

 the giains and |)lales of I he 

 bisilicate. The refraclixe indices 

 of ihc needles are somewhat 

 less than those for pure Ll.,Slü^\ 

 we fonnd e.g. : 1.595 and 1.5(it) 

 ill the same individuals. 



<j). 71.17,, 'S/VA, (=-- 54.9 Mol. 

 Proc). 



The quantity of the metasili- 

 cate is considerably increased ; 

 Fig. 1 ïi. 78,8 Weight Proc. SiO,. (Enlarg. 5UX). for the remaining part Just as ƒ. 



li). 66.7V„ SiO, (=49.7 Mol. Proc). 



Homogeneons. It is the Li,SiO^, with all properties, formerly in- 

 dicated. The axial angle seems to be rather small. 



i). 63.97o Si(K ^=:46.7 Mol. Proc)- In general lines this pre|)aration 

 resembles the former; locally small grains of the orthosilicate, 

 with its weaker birefringence, but stronger refraction, are visible. 



