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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. 



Crystalline 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. 4j 



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. d 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 X 



