GLUCINA. 



377 



Fig. 412. 



Fig. 409. of Figs. 409, 410, 41 1 and 412. In Fig. 



409, two opposite shorter terminal edges 

 are replaced by the plane i. The striae 

 being perpendicular, and the axis of re- 

 volution being parallel to the edge formed 

 by the meeting of the planes T and i, a 

 revolution of 180° would give the form 

 Fig. 401. Two of these crystals would 

 give the right rhombic table represented in 

 the lower part of Fig. 404 ; and again, 

 three of tkese form the regular six-sided 

 prism. The crystal 402 is in like manner formed by a similar revolution of a crystal like 

 that represented in Fig. 410, in which all the shorter terminal edges are replaced by the 

 planes i, being a crystal of the same form as Fig. 399. The two crystals Figs. 401 and 402 

 will produce the form Fig. 403, and three of the latter united give that of the six-sided prism 

 Fig. 405. In Fig. 407, one of the crystals is wanting. Six of the forms Fig. 402 give that 

 represented by Fig. 406, which is occasionally observed at this locality. The compound 

 crystal Fig. 408 is marked by strias as represented in the cut, and I suppose it to be produced 

 by the union of four crystals similar to those represented in Fig. 401, and two formed by the 

 revolution in the direction of the dotted line, Fig. 411, so as to give that represented in Fig. 

 412. The angles of all these crystals, whether single or compound, are 60° and 120°. 



Fig. 413 is introduced from Shepard's Mineralogy. It is more rare 

 at the Greenfield locahty than either of the preceding. According to 

 that author, in this case three prisms, similar to Fig. 410, cross each 

 other, and the prisms project at each end beyond the face of compo- 

 sition. It will be observed that the direction of the striae is different 

 from that in the preceding figures, and I infer therefore that its com- 

 position is different. 



In Connecticut, chrysoberyl occurs at Haddam, where it is asso- 

 ciated with the minerals for which that locality is so celebrated. 



Fig. 413. 



MiN. — Part II. 



48 



