32 Mr. William Phillips's Description 



The primitive Crystal and Its varieties. 



Fig. 1 is the primitive crystal ; the angle formed by the meeting 

 of the two faces PP has been ascertained by Haliy to be 109d. 28'. 

 16". Fig. 2 is the result of a * decrease on one face of the upper, 

 and on the opposed face of the lower pyramid. This crystal has 

 aptly been called the segment of the octohedron, as the explanatory 

 fig. 3, will evince. Fig. 4 is the primitive crystal elongated ; this 

 elongation arises, as is obvious, from a regular increase of the crystal- 

 line laminae on one face of the upper pyramid, and on that face of 

 the lower to which It is united at their common base. Fig. 5, is the 

 same occurring in capillary crystals. Fig. 6 differs from fig. 4 in the 

 upper pyramid only ; on the already increased face of which, a still 

 further increase of lamlnse has taken place, as well as a similar depo- 

 sition on the opposite face of the same pyramid. Fig, 7 is produced 

 by an increase on one face of the upper, and on one face of the 

 lower pyramid of fig. 4, as will be obvious on consulting fig. 8. 

 Fig. 9 is the consequence of an increase on two opposed faces of the 

 upper, and on the other two opposed faces of the lower pyramid of 

 the primitive crystal, as will be seen by fig. 10. Fig. 11 is the result 



* In the present imperfect state of mincralogical language, it is difficult on every 

 occasion to find terms by which even facts can be accurately defined. For instance, in 

 that modification of the octohedron, where the solid angle is wanting, and which though dif- 

 ferlngin form from the primitiveCrystal, can scarcely be called an imperfection in crystalli- 

 ration, there is no term in use justly descriptive of the fact. The terms truncation and 

 decrease are obviously inaccurate. I have used the latter as perhaps the least excep. 

 tionable. It is with deference to the opinions of the Count de Bournon, I venture to 

 observe that the term retro gradation lately adopted by him seems equally objection- 

 flble with either of the preceding. 



