386 



Transactions. — Geology. 



In 1868 a specimen, also consisting chiefly of sulphate of alumina, was 

 forwarded for identification by Mr. G. Eichardson from Eancowers Island, 

 Manawatu. 



Alum, E S + (-Ah; -Fe) S 3 + 2-i H.— The first mention of the occur- 

 rence of this mineral in New Zealand is by Dr. v. Hochstetter (New Zea- 

 land, 1863, Eng. ed., p. 408), who states that on Puai Island, in the 

 Eotomahana Lake, he found films of fibrous alum under cakes of siliceous 

 deposit. 



Dr. Hector mentions its occurrence as a product of decomposition of 

 pyritous shale at Waikouaiti (Jurors' Eep. N.Z. Ex., 1865, p. 35), and 

 (p. 421) he states that aluminous shale is generally associated with the 

 brown coal formation. An analysis of some shale that had undergone 

 natural decomposition, and was covered with an efflorescence of alum, 

 gave — 



Sulphate of alumina . . 



11-80 



„ ,, protoxide of iron 



5-27 



,, „ sesquioxide of iron 



traces 



„ ,, lime 



1-31 



,, „ soda and potash 



. 14-60 



Chlorides 



traces 



Insoluble in water 



. 33-30 





. 33-72 



10000 

 the insoluble matter being principally angular fragments of schist. He also 

 mentions (Jurors' Eep. N.Z, Ex., 1865, p. 438) the occurrence of potash 

 alum in shale at Tokomairiro, and the Auckland Local Committee exhibited 

 specimens of alum from Eotomahana. 



In 1866 Mr. T. E. Hacket collected some magnesian alum from D'Urville 

 Island, where it is found as delicate acicular crystals, of a pure white colour, 

 grouped in large botryoidal masses, the exterior surfaces of which are of a 

 yellowish colour from the presence of basic sulphate of iron. It has a sour 

 and slightly astringent taste, is very soluble in water and intumesces on the 

 application of a gentle heat. In the blowpipe flame after desiccation it is 

 infusible ; displays considerable incandescence and yields the reaction of 

 soda. Its composition is — 



Alumina . . . . . . . . 10-40 



Ferric oxide 

 Lime . . 

 Magnesia 

 Soda . . 

 Sulphuric acid 

 Hydrochloric acid 

 Water 

 Insoluble in water 



1-11 



•50 



5-46 



•41 



37-40 



traces 



42-72 



2-00 



100-00 



