

COMPOUND MINERALS. 01 



of crystals ; which although they are founded in the nature of the 

 individuals themselves, yet cannot be employed to any extent in 

 the discrimination of minerals. The extraneous imitative forms do 

 not depend upon the natural forms of the individuals, but merely 

 upon the shape of the space previously existing, and are, therefore, 

 entirely accidental. 



. 76. IMITATIVE SHAPES ORIGINATING IN THE GROUPES 

 OF CRYSTALS. 



The imitative shapes which originate from the groupes 

 of crystals, are loose or imbedded, and more or less dis- 

 tinctly globular, or spheroidal masses. 



If the individuals connected with each other become very mi- 

 nute, and at the same time unite with each other into a groupe of 

 crystals, globular forms result, which are sometimes very perfect, 

 at others very imperfect. Their surface is drusy, or covered with 

 minute asperities, where it has not been disturbed in its formation, 

 or by subsequent accidents. When broken open, the direction of 

 the constituent individuals becomes apparent, and in most instances 

 corresponds to the direction of the radii of a sphere, beginning in the 

 centre and terminating at the surface. Imbedded globular shapes, 

 like imbedded crystals, are complete on all sides, and ler.ve an im- 

 pression of their form in the mass from which they have been de- 

 tached. Instances of imbedded globular shapes occur in Iron Py- 

 rites, Chlorophaeite, &c. When globular masses are attached to 

 one another, they may produce reniform and botryoidal shapes, as 

 in Malachite ; but such instances are rare, and require to be distin- 

 guished from those described in (. 77.) 



The loose or imbedded globular shapes differ from grains and an- 

 gular masses, inasmuch as they are not simple minerals. 



. 77. IMITATIVE SHAPES ARISING OUT OF THE GEODES 

 OF CRYSTALS. 



There are three different kinds of imitative shapes re- 

 sulting from geodes of crystals : 1. Those in which the in- 

 dividuals spring from, or are attached to, a common point 



