51 



outlines of course also become curved, so that they could only 



be approximately adjusted. A great number of adjustments and 



readings have been made, and of the values thus obtained the 



means have been taken. The measurements found in this 



way are 



(101) : (lOT) = 90° 5' and (Oll) : (OlT) = 85'^ 4'. 



From them the following axial ratios for ancylite are 



calculated: 



а:Ъ:с = 0,916 : I : 0,9174. 



The larger and better developed ancylite crystals generally 

 occur isolated from one another on the substance to which 

 they are attached. The occurrence of a number of individuals 

 grown together into small groups or druses is rare. They 

 are often developed almost on all sides, being attached in rows 

 along thin needles of ægirine or imbedded in a loose felted 

 mass of such needles. Owing to the curved form of the faces 

 and the circumstance that the corners and edges are more or 

 less rounded the crystals get a somewhat sphere- like habit. 



The highest degree of curvature is exhibited by the faces 

 belonging to the prism of the second order, e; further they are 

 generally almost quite dull. With the aid of a magnifier one 

 finds that this dullness is due to the fact that the faces are 

 divided into a number of minute triangular elements orientated so 

 that their outlines are parallel to the outline of the whole face. 

 The faces belonging to the prism of the first order, d^ are 

 more even than the others. They are also often tolerably bright. 

 However, a division into diminutive triangular faces is obser- 

 vable also on them; but this division is here far less distinct 

 than on the other faces. 



The smaller, less distinct crystals are generally more 

 rounded than those now described; they are either nearly sphe- 

 rical or have the form of irregular grains. They usually form 

 continuous crusts coating the surfaces of feldspar or ægirine 

 individuals. Masses of small ancylite crystals grown together 



