194. 



Form. 



The inconceivably minute particles — molecules — of which minerals are 

 made up are arranged sj-mmetrically, or may be aggregated together 

 without following any definite plan. In the first case, the minerals ai-e 

 said to be "crystalline," and have a tendency to occur in definite geometrical 

 forms — crystals. Some of these forms will be exhibited elsewhere. In the 

 second case there is no s\Tch tendency. 



In this place are illustrated some of the characteristic forms assumed by 

 minerals when non-crystalline, or when, although crystalline, no definite 

 form is evident. 



Illustrations of characteristic forms : — 



Dendritic or arborescent : manganese oxide. 



Tabular ; spec2da7' iron. 



Platy or leafy : native copper. 



Wiry : native ailver. 



Mossy : native copper. 



Capillary (hair-like) : millerite. 



Coralloidal : aragonite. 



Stalactitic : calcite. 



Mammillated : malachite. 



Botryoidal (like a bunch of grapes) : manganese oxide. 



Reniform (kidney-shaped) : hematite. 



Granular : galena, magnetite. 



Acicular (needle-like) : antimonite. 



Fibrous : gyx>sum, asbestos. 



Eadiated : natrolite. 



Micaceous : hematite. 



Foliated : molybdenite. 



Nodular : marcasite. 



Amygdaloidal : aragonite. 



Geode : quartz. 



Matted (reticulated or interlaced) : chalcotrichite. 



Amorphous : ^cad. 



