53 



crystal, and its outline is, consequently, rectangular. The ex- 

 tinction is parallel to the sides of the section and still more 

 undulating than in the foregoing sections. The direction of 

 the greatest velocity of light coincides with the crystallographical 

 «-axis. 



From the foregoing it is clear that the plane of the optic 

 axes of the ancylite is parallel to the third pinacoid {OOl}, and 

 that the acute bisectrix coincides with the crystallographic b- 

 axis. As the latter also is the direction of the smallest velocity 

 of light, the ancylite is optically positive. 



The sections show high interference colours , and even 

 tolerably thin sections show white of a higher order. The 

 mineral, consequently, is strongly doubly-refracting. Owing to 

 the unfavourable condition of the material it has not, however, 

 been possible to determine the indices of refraction. 



The hardness of ancyhte is = 4,5. The mineral is 

 possessed of a certain degree of toughness, so that, when it 

 is crushed, the splinters do not fly about. The fracture is 

 splintery. Cleavage not observable. 



By weighing in benzole the specific gravity of the mineral 

 has been found to be = 3,95 (Mauzelius). 



Before the blowpipe in the forceps ancylite is infusible, 

 and, as the carbonic acid is expelled, it assumes a brown 

 colour. Heated in the closed tube it gives off water abundantly. 

 Moistened with hydrochloric acid it imparts an intense red 

 colour to the flame. It is readily soluble in acids with 

 evolution of carbon dioxide. 



The material for the analysis was taken from the crusts 

 of small yellowish green crystals above mentioned. The crusts 

 were crushed and the minute crystal grains selected by hand- 

 picking with the aid of a magnifying glass. The material used 

 may be regarded as perfectly pure. For determining the carbon 

 dioxide 0,5514 gr. was used, and for the determination of the 



