248 Mr. William Phillips on the 



if we would methodically seek to obtain the nucleus. By following 

 this plan, I have occasionally succeeded by the assistance of the 

 pince r s, or by sharply striking a piece of steel long enough to 

 extend across the surface, with its edge placed on the quartz in 

 the direction of its laminae. That neither of these plans often 

 succeeds, and I know of none more effectual, is to be attributed to 

 the great brittleness of the substance, which renders it liable, even 

 when struck in the direction of its natural joints, to present frag- 

 ments wholly irregular, or in various degrees approaching the 

 conchoidal form. Quartz may however, though with still greater 

 difficulty, be split in two or three directions which are not parallel 

 with the planes of the primitive rhomboide. 



Zircon*. 

 Fig. 1. 



Several substances, not essentially differing in composition cr in 

 their crystalline form, are by Hauy arranged under the general 

 term zircone. Their primitive crystal is described in the Tableau 

 Comparatif, as an obtuse octohedron with square bases admitting 

 of regular fracture parallel with sections passing through the apices, 

 and through the centers of the edges D. D. The jargoon of Ceylon 

 does not admit of being split with the same ease as the hyacinth of 

 France, of which I have obtained and possess regular cleavages in 

 the directions mentioned by Hauy, and also parallel with sections 

 that would divide the octohedron into four parts by passing along 

 all the edges of both pyramids. 



The fractures in the direction of the primitive planes were most 

 difficultly obtained, and though numerous, are not sufficiently 



