40 NEW YORK STATE MUSEUM 



Inclusions 



Foreign bodies inclosed within a crystal are described under 

 the general name of inclusions. They may be solid, liquid or 

 gaseous in nature and organic or inorganic in origin. In gen- 

 eral, inclusions result from rapid crystallization, as in the case 

 of the calcite crystals shown in pi. 1 2 ; these show the typical 

 rhombohedron of calcite, though containing a large percentage 

 of the quartz sand carried by the solution from which they were 



crystallized. 



CnjstalUn e aggregates 



Under this head are included the great majority of mineral 

 specimens made up of aggregates of imperfect crystals. Many 

 masses of material which appear to have no crystalline struc- 

 ture can be proved by optical and other physical tests to be 

 composed of crystalline grains. 



1 Columnar structure. Minerals possessing a columnar or 

 fibrous structure present the appearance of bundles of slender 

 columns. 



parallel columnar, example beryl, pi. 2 :1 



bladed, example cyanite, pi. 2 2 



fibrous, example serpentine (chrysotile) pi. 3 X 



2 Lamellar structure. The mineral is composed of layers or 

 leaves. 



curved lamellar, example talc, pi. 3 2 



foliated or micaceous, example muscovite, pi. 4 2 



3 Granular structure. The crystalline particles consist of 

 angular grains of about the same size. 



coarse granular, example magnetite, pi. 4 2 

 fine granular, example dolomite (marble), pi. 5 1 



4 Imitative shapes. The arrangement of masses of imperfect 

 crystals often give rise to forms which resemble those of ani- 

 mate nature. The most important terms used to describe such 

 forms are: 



reniform, kidney-shaped, example hematite, pi. 5 2 

 botryoidal, composed of globular individuals resembling a 

 bunch of grapes, example quartz (chalcedony), pi. 6 2 



