121 



the last-mentioned face, which is always very narrow, has not 



been observed before in heiilandite; it is determined by the 



angle : 



Average v„--„f ^ Number of Calculated 



, Variations . , 



value measurements value 



r:c={50l}:{00l} = 77^^54' 76°53'— 78°53 4 77°o8i' 



The comparatively large variations in this angle are mostly 

 caused by the faces both of >'{50l} and c{00l} being usually 

 somewhat broken and facetted so that, as a rule, several di- 

 stinct reflexes are produced by them ; the form must, however, 

 be considered to have been definitely determined. 



These small crystals are perfectly clear and transparent 

 with very bright faces. 



Mount Henry, east side. Grey fine-grained basalt, which 

 was found here, contains a few cavities almost completely filled 

 with heulandite. Very few crystals are found, their length 

 being about 2°^. The following combinations occui": ^{Oio}, 

 c{00l}, ^{20t}, s{20T}, ni[]l0}. The colour is a deep red. 



Кар Brewster. Here the heulandite is found in two very 

 different forms : 



1) It occurs with stilbite in a single amygdaloid, probably 

 obtained from tufa. The heulandite crystals are small 

 (1 — 2°^), few in number and are interspersed among the 

 large stilbite crystals. They have the form of plates parallel 

 to è{lOO}, bordered by c{00l}, ^{20l} and s {20T}. The 

 faces are bright and fairly well-devel- 

 oped; the crystals are of a pale reddish ^-^^^c • .^-^^^^ 

 colour. / ^ I \ 



2) .Many heulandite crystals were found in j\ /ч: Ч /* •.- 



cavities in a dark brownish very fine- [/ XJ ;.••■"" 



grained basalt. The crystals are small 1 "^ \ / 



(1—2™'"), well-developed and unaccom- \\. ■■'''A'^^^ 



panied by other zeolites. Sometimes ^. „ n ■ j-. 



•^ Fig. 8. Heulandite; 



the space between the crystals is filled Кар Brewster. 



