PAPER READ. 



NOTES ON THE OCCURRENCE OF STILBITE IN THE 

 ERUPTIVE ROCKS OF JAMBEROO, N.S.W. 



By B. G. Engelhardt. 



(Plate i.) 



This zeolite is mentioned by Prof. Liversidge, M.A., F.R.S., as 

 having been found in a few New South Wales localities,* but, as 

 far as I am aware, it has not yet been reported from Kiama and 

 its vicinity. While collecting specimens of the different eruptive 

 rocks in the neighbourhood of Jamberoo, I observed a bright red 

 mineral in some pieces of a dense, fine-grained basalt, obtained 

 from the northern flank of " Wallaby Hill," an eminence on the 

 south of the Minnamurra Valley. Shortly after, I found the 

 same mineral in a porphyritic dolerite, not far from the locality 

 just mentioned. 



In either the basalt or dolerite, the mineral in question occurs 

 almost invariably in more or less circular crystalline masses, from 

 5 to 100mm. in diameter; but in one instance it was found to 

 have filled up a small fissure in the surrounding rock, having 

 spread itself as a crust of small crystals over the adjacent surfaces 

 of the matrix. The cleavage planes of the individual crystals 

 in the stellate groups (in which form the mineral occurs most 

 frequently) show the characteristic pearly lustre of stilbite. The 

 crystals are flat prisms whose cleavage is so perfect, parallel to 

 their shorter planes, that it was easy to split off laminse sufficiently 

 thin and transparent for microscopical observation by transmitted 

 light. 



In colour the mineral varies from a yellowish-white to purple- 

 brown, but the most usual tints are flesh-red, scarlet, and brick-red. 



* Minerals of N.S.W. , 1888, p. 187. 



