.184. OF COMPOUND MINERALS. 257 



shapes. The first of these consist of individuals which are 

 perpendicular to every point of a straight cylindrical or linear 

 support in its whole circumference, as appears from many 

 examples in prismatic Iron-ore, in prismatic Iron-pyrites, 

 where the composition commonly is still observable, and in 

 the varieties of rhombohedral Quartz, called Calcedony, 

 where the individuals no longer can be distinguished. On 

 a very large scale they are not uncommon in limestone 

 caves, and consist of varieties of rhombohedral Lime-ha- 

 loide. The coralloidal shapes consist of individuals inclined 

 at an angle to their support, which, although linear, is not 

 straight ; they are fixed upon this support in every part of 

 the circumference, exactly as is the case in the stalactitic 

 shapes. This vsort of imitative shapes occurs not unfre- 

 quently in prismatic Lime-haloide, particularly in those 

 varieties which have been called Flos-ferri. 



There occur many more imitative shapes in nature than 

 those contained in the preceding examples, and many more 

 have been distinguished and described by mineralogists. 

 But these few examples will be sufficient to shew the me- 

 thod of explaining all forms similarly composed. 



. 184. AMORPHOUS COMPOSITIONS. 



If the mass, formed by the junction of several 

 individuals, is not only of an irregular shape, but if 

 even in this we cannot trace any resemblance with 

 the shape of another body, the mineral is said to 

 be massive. 



Massive minerals are amorphous irregular compositions of 

 individuals of the same species, which are in contact with 

 each other on all sides. The difference between massive 

 minerals, and those forms resulting from the groupes of 

 crystals, which deviate more or less from the spheroidal 

 shape, consists merely in the strong adhesion of the fyr- 

 mer to the surrounding masses of other species. It is 

 formed, however, and assumes a shape corresponding to 



