118 



Twinning is extremely rare among the tainiolite crystals; 

 only a single twin crystal has been found. It is a contact twin, 

 represented by Fig. 10, Plate III. One of the individuals crosses 

 the other at an angle of 60° ; their composition face is the third 

 pinacoid. It looks as if one of the individuals were lying loose 

 on the other. This form of twinning is exactly the same as 

 that occurring with epididymite. 



The mineral is colourless and usually pefectly clear. The 

 thicker individuals, however, show a distinct tinge of blue. 

 Lamellae parallel to the third pinacoid show in parallel polarized 

 hght total extinction parallel to the second pinacoid, with which 

 also the plane of the optic axes is parallel. The acute bisectrix 

 emerges in front of the c-axis, making an angle of about 6° 

 with it. The apparent angle between the optic axes is per- 

 ceptibly smaller than with polylithionite. With the aid of the 

 micrometer ocular and Schwartzmann's scale the angle 2E 

 was found to be about 50°. The double refraction is negative 

 and not very strong. 



The hardness of tainiolite could not be determined with 

 accuracy. There is, however, no reason for assuming it to 

 differ essentially from the hardness of other species of mica, i. e. 

 2,5 — 3. The cleavage of the mineral is as eminently perfect« 

 as in muscovite. If the strips are gently bent to a slight extent, 

 they will resume their original position. The limit of elasticity 

 may, however, easily be exceeded, for when bent with some 

 force the individuals will remain curved. 



By weighing in benzole the specific gravity of the mineral 

 has been found to be 2,86 (at a temperature of 16° С , Mau- 

 zelius). 



Before the blowpipe in the forceps the mineral fuses easily 

 to a colourless blebby glass colouring the flame intensely red. 

 It is completely, but somewhat slowly decomposed by hydro- 

 chloric acid. 



A.s already mentioned, it has been troublesome to pro- 



