CRYSTALLOGRAPHIC STUDIES OF BARITE 



BY HERBERT P. WHITLOCK 



The following crystallographic notes on three hitherto undescribed 

 occurrences of barite are submitted, not because these localities 

 furnish crystals which are unique in new forms or rare habit, but 

 because it is the firm conviction of the writer that all contributions 

 to the study of species rich in forms are of value in shedding light 

 on the problems involved in crystal habit. 



The specimens which form the basis of these studies are from the 

 general mineral collections of the New York State Museum, and 

 have been acquired by gift and exchange during a period covered 

 by the last eight years. 



i Barite from Five Islands, Nova Scotia 



The series of crystals which furnished the material for this note 

 were obtained from a single specimen (no. 719.11) acquired by 

 exchange from the Museum of the University of Toronto, and 

 bearing the label as above. The specimen consists of a crested 

 aggregate of crystals of uniform habit, tabular parallel to the basal 

 pinacoid, and showing on the termination, in close proximity to the 

 zone of the macrodomes, a series of somewhat dull but well-defined 

 planes which correspond to several macropyramids new to the species. 



Habit. The crystals, some of which are 30 mm by 20 mm in 

 size, show considerable dome development, in habit somewhat 

 resembling the combination from Sajohaza, Hungary, described by 

 Zimanyi. 1 The planes of the prism m (no) are developed to a 

 considerable habit, the zone [100:001] being emphasized by two and 

 sometimes three pyramids, present in minute development. A 

 feature of the habit which also suggests the Sajohaza occurrence 

 mentioned above, is the reentrant angles formed by the parallel 

 group development or oriented growths (Fortwachsungen) of the 

 planes of (165). It was at first suspected that these growths, which 

 are shown in the shaded section accompanying figure 1, might be 

 due to twinning, but an examination of the optical behavior of the 

 crystals proved that this was not the case. Figure 1, which shows 

 the habit of these crystals, is drawn with the a and b axes reversed 

 with respect to the usual orientation. 



1 Zimanyi, K. Foldt., Kozol. 1909. XXXIX, fig. 8. 



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