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Topaz. 



Fig. I. — A right rhomboidal prism with angles of 124° 22' and 55° 38'. 

 Fig. 2. — An eight-sided prism terminated at each end by a four-sided pyramid. 

 Fig. 3. — A similar prism terminated at each end by two broad and four smaller 

 planes. 



Fig. 4. — A similar prism terminated at each end by two broad and five smaller 

 planes. 



Tourmaline. 



Fig. 1. — The primitive crystal, an obtuse rhomboid. 



Fig. 2. — ^A nine-sided prism, terminated at one end by six planes, and at the other 

 by three. 



Fig. 3. — Shews the lower end of Fig. 2. 



Fig. 4. — A nine-sided prism terminated at each end by six planes, the broader and 

 narrower of which are set alternately on the edges and sides. 

 Fig. 5. — The lower end of Fig. 4. 

 The ends A A of Figs. 2. and 4. are the seats of the vitreous or positive, and B B 

 of the resinous or negative electricity, when the crystals are gently heated. 



THE £XD. 



