58 TERMINOLOGY. 



<>. 54. IRREGULARITIES FROM CONTACT WITH OTHER 

 INDIVIDUALS. 



There are two sorts of contact by which the regularity of 

 crystals is affected ; viz. 1. contact on all sides, 2. contact 

 only by some of their parts. 



Crystals surrounded and inclosed by the solid mass in which they 

 are found, or in which they have been formed, are in contact with 

 this mass on all sides. This mass may either be of the same sub- 

 stance with the crystals, or it may be otherwise. In the first in- 

 stance, the regularity of the form is scarcely ever perceptible. One 

 individual prevents the other individual, by their contact, from as- 

 suming that regular form, which under other circumstances, is pecu- 

 liar to it; and we see individuals in these cases assuming their regu- 

 lar shape only, when some cavity or empty space occurs in the mass, 

 which enables them to emerge from contact with -other individuals. 



If the mass, which surrounds a crystal, is not of the same nature 

 with the crystal, the regularity of the latter is not so liable to be im- 

 paired. A crystal, under such circumstances, is said to be imbedded; 

 and when disengaged from its bed, is termed a loose crystal. Crys- 

 tals of this kind may be taken out of the mass which surrounds them, 

 and if they do not cohere with any particles of the mass, a smooth 

 print of their form w r ill remain. Loose crystals, if not imperfect in 

 some other, way, may be considered as the most perfect productions 

 of inorganic nature. Such crystals, however, are comparatively 

 rare. More commonly, they are imperfectly formed of themselves, 

 or they have been rendered imperfect by their contact with the sur- 

 rounding mass. Those individuals, whose dimensions are nearly 

 equal, appear as rounded or angular masses, and bear the name of 

 grains or angular masses, both of which, are nothing else but im- 

 perfectly formed crystals. Pargasite is a good example of crystals 

 of this sort. Besides these imperfectly formed crystals, there exist 

 a great many others, which likewise assume, more or less, a globu- 

 lar or angular shape. These, however, must carefully be distin- 

 guished from real grains and angular masses, because they are not 

 simple but compound minerals. (. 15.) 



Crystals which are formed in an empty space, and adhere only 

 with some of their parts to the support, which in most cases is dif r 

 ferent from the mass of crystals, are termed implanted crystals. 



