101 



quite irregularly; so far as can be seen because of their small- 

 ness, they consist of fluid inclusions. The speciOc gravity has 

 been determined by Thoulets solution; for the purest pieces it 

 is 2"5T8, while it decreases gradually with the increasing 

 quantity of the above named inclusions; for [one of the more 

 impure pieces it has been determined at 2*463. 



Gyrolite is, as stated by Descloizeaux ^) optically negative. 

 1 have succeeded in determining the indices of refraction by 

 the total reflectometer, using a very even face of c{000l}; the 

 boundary lines were quite sharp and distinct; I have found: 



w = l'564o. 

 г = ГЬо90. 



For the analysis I have selected cleavage pieces of the 

 most perfect transparency; as the mineral is always overgrown 

 with wery small crystals of calcite I have washed it with dilute 

 acetic acid. The analysis was made by cand. polyt. Chr. Chri- 

 stensen with the following result: 



Of the water 2*45 pCt. goes away by heating to 100°; no 

 trace of fluorine is found. 



As will be seen the quantities of the different constituents 

 do not stand in any simple relation to each other. The com- 

 mon formula for gyrolite, Z B.,0, 2 CaO, Z SiOo, cannot be 

 adopted here, as the quantity of water is but half so large as 

 required. What part the alumina plays is not easy to see; it 

 cannot, I think, belong to any foreign mineral e. g. feldspar as 



') N. R. 13, 18R7. 



