WATER OF CONSTITUTION. 



nesium hydroxyl groups. Serpentine has absorption bands at 1.4, 3, 5, 

 6.6, 74, 8.1, and 8.5 /*. 



(Subtransparent; f = 0.06 mm. Curve c, fig. 36.) 



In talc, water is expelled at red heat ; from its stability with acids it is 

 considered an acid metasilicate. From the investigations of Clarke and 

 Schneider (loc. cit.) no hydroxyl groups were inferred, and the trans- 



IOOfo 



10 



I ? 3 4 5 



/ 



FIG. 37.-Epidote. 



mission curve does not show a band at 3 ju,. Talc has absorption bands 

 at 5-6, 5-95> and 7.15/4. 



EPIDOTB (Ca,(A10H) (Al,Fe).(SiO).). 



(Cleavage piece parallel to c for curve a, t = o.2i; section perpendicular to axis 



for curve b, t = o.og. Fig. 37.) 



The chemical formula of this mineral is variously written, and it may 

 contain hydroxyl groups. The iron may be present as FeOH. 



