Feb. 1900. Crystal Forms of Calcite — Farrington. 233 



These came from the Blakie No. 2 mine. The crystals which may 

 be designated as Type No. 2 are characterized by a deep amber 

 yellow color ranging to colorless. They come from the Crystal 

 Cave, Ino mine. These two mines are quite near one another, and 

 are both located in Leadville Hollow, within the city limits of Joplin. 



FORMS OF LARGE CRYSTALS. 



Type I . — Crystals of this type are very simple in form. They 

 are made up of the common scalenohedron v, -(-R3,* truncated by 

 the flatter scalenohedron /, -\-}(K^. The average development of 

 the forms is illustrated in Fig. 1, PI. xxviii, it being drawn one-half 

 size from one of the crystals in the Museum collection. Such a 

 size is usual to crystals of this type. The following are averages 

 of measurements of several angles on crystals of this type, as made 

 with a contact goniometer: 



23i~4= 



3"i24= 



2131 = 



ion = 



3~i2~i = 



23U = 



101*1 = 30 



The surfaces of the crystal planes on these crystals are, in gen- 

 eral, flat and bright and of uniform lustre. They are, however, more 

 or less irregularly marked similar to the planes shown in Fig. 2, 

 PI. xxviii, and reentrant angles resulting from abortive terminations 

 often occur. While the crystals are often doubly terminated, as 

 illustrated in the figure, more commonly only about half of the com- 

 plete crystal form is present, the plane of attachment being a rhom- 

 bohedral or a basal plane. Numerous planes of rhombohedral cleav- 

 age pass through the crystals, and the light reflected from them often 

 brilliantly illuminates the interior. Many crystals are also often iri- 

 descent from interference colors produced by parting along cleavage 

 planes. Irregularly shaped grains of marcasite from one to two milli- 

 meters in diameter often occur scattered through the outer layers of 

 the crystals. Other associated minerals, often well crystallized and 

 found more or less in contact, are galena, dolomite and chalcopyrite. 

 A group of this character, now in the Museum collection, is shown in 

 the frontispiece. 



*The letters used are Dana's. 



