142 



RECORDS OF THE AUSTEALIAN MUSEUM. 



from this the forms were identified by means of Penfield's 

 protractors and the identification was confirmed by calculation of 

 the normal angles. All the faces are small with the exception of 

 t (111) which gives an excellent image, and a peculiar rounded 

 face which could not be determined but is possibly ,/• (301) ; the 

 pinacoid h (010) is very small when present. 



The table contains some of the results of measurement com- 

 pared with the theoretical angles given by Goldschmidt. 



DATOLITE. 



CoLEBRooK Mine, Dundas, Tasmania. 



(Plate xxxiii.). 



This mineral was first obtained in sinking a shallow shaft in 

 the western poi^tion of the limurite outcrop. ^"^ It is found 

 associated with axinite, calcite and other minerals as already 

 described under axinite, and sometimes occurs in large brilliant 

 crystals. It is colourless, greenish or yellowish. 



Crystallograjyhy. The crystals have mutually interfered during 

 growth, but one small projecting crystal was found and measured. 

 This crystal is shown in ideal and actual development in PL xxxiii., 

 figs. 1-4 ; fig. 5 shows the distribution of forms and the chief 

 zones. 



The habit of the figured crystal seems characteristic so far as 

 can be judged by inspection of others ; it is prismatic by exten- 

 sion parallel to the a axis and measures about 6 mm. in length. 

 It is fairly rich in forms, but as is usual with datolite many of 

 the faces are wavy and give poor reflections ; the three faces i 

 (212), 77 (231), and x (102) are dull and were measured in the 

 position of maximum illumination. 



As in the case of axinite, Goldschmidt and Dana choose 



Petterd— Proc. Eoy. Soc. Tas., 1897 (1898), p. 63. 



