119 



MINERALOGICAL NOTES. 



By D. Mawson, B.E., B.Sc. 



[Read May 7, 1907.] 



Plate XXI. 



Contents. 



Page. 



1. Baiytes Sand Crystals: Hallett Cove ... 119 



11. Radial-Nodular Barytes : Brighton 120 



111. Gypsum: Southern Yorke Peninsula ... 120 



IV. Gypsum: Patawalonga Creek 122 



V. Gypseous Tufa: Paratoo 123 



VI. Amazonstone : Olary ... ... ... ... 123 



VII. Stolzite: Olary 123 



VIII. Chrysotile: Tumby Ba^^ 123 



IX. Wollastonite : Tumby Bay 124 



I. Barytes Sand Crystals. 



Crystalline sandy nodules occur shoaded on the surface 

 above the cliffs immediately north of Hallett Cove. Their 

 occurrence has long been known, though their composition is 

 generally stated in local collections as "pseudomorphs after 

 selenite." 



On first encountering these crystals, the author was 

 struck by their high specific gravity ; chemical tests were 

 therefore instituted, and an analysis showed a typical individ- 

 ual to contain approximately 35 j^er cent, of barium sulphate. 



Further investigations revealed its presence, as optically 

 continuous barytes, cementing the remaining 65 per cent., 

 which is composed of ordinary sand grains. Calcium sulphate 

 was found present only in negligibly small quantity. 



The aggregates prove, therefore, to be "barytes sand 

 crystals," analogous to the well-known "calcite sand crystals" 

 from Indian Reserve, United States of America. 



The exact location of the occurrence is above the cliffs at 

 Black Point, and for some eight chains northward, following 

 near the lower margin of the Miocene limestone. A very com- 

 plete geological section at Black Point is detailed in one of 

 the Aust. Ass. Adv. Science Glacial Research Committee Re- 

 ports. i A considerable thickness of alternating rusty and 

 ysllowish sandy, and chocolate and reddish shaly beds are 

 there shown to compose the upward extension of the Permo- 



(DPl. i., — Brisbane, 1895. 



