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PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 71 



rock. The former crystals have the habit illustrated in Figure 17. 

 The measurements obtained on such a crystal are as follows : 



Measurements of apatite, Figure 17 



Optically this apatite is uniaxial with the refractive index to=1.634. 



BARITE 



Barite is present in a single specimen (No. 84569) where it coats 

 opposite surfaces of a mass of dense metamorphosed sedimentary 

 rock. The crystals are flattened as though they had grown in a con- 

 stricted space and reach a maximum size of about 8 mm. Crystals 

 split on the basal cleavage show zoning in more and less transparent 

 layers parallel to the unit prism. The crystals are very poorly 

 defined and are bounded only by the prism m(llO) and the base 

 c(OOl). This gives them a rhombohedral appearance and they 

 greatly resemble chabazite. 



EXPLANATION OF PLATES 

 Plate 1 



Upper left : Flattened barite crystals of rhombic outline resembling chabazite 



coating surface of rock along fracture. 

 Upper right : Twinned crystals of diopside lining cavity in diopside hornfels. 

 Lower: Coarse crystalline columnar mass of scapolite partially replaced by 



scolecite. 



Plate 2 



Upper : Perfect crystals of vesuvianite lining cavity in diopside rock. 

 Lower: Rhombohedral crystals of chabazite, crystals of vesuvianite and a 

 rosette of stilbite in a vug in massive diopside rock. 



o 



