404 E. S. Simpson — Laterite in Wedern Australia. 



ai-e parth" filled with similar material to the nodules, partlv unfilled. 

 Earely (e.g. Lone Hill, Kalgoorlie) some of the more ferruginous 

 laterites are devoid of concretionary structure, whilst still containing 

 numerous visible pores. 



The composition of some typical laterites is given in the 

 accompanying table : — 



COMPOSITION OF WEST AUSTEALIAN PEIMAEY LATEEITES. 



These analyses, though so many of them are incomplete, are an 

 assistance in unravelling the mineral c|)mposition of the laterite. 



The iron is undoubtedly present as limonite, 2 Fe., O3 . 3 H,, 0, in 

 many of them, e.g., Kalgoorlie (4), Smith's Mill, andWongan Hills. 

 Turgite, 2Fe2 03.H.2 0, is, however, just as common, particularly in 

 laterites from the interior, such as Kalgoorlie (1), (2), and (3), and 

 Coolgardie. Its presence, suspected from the results of the analyses, 

 was readily confirmed by the decrepitation of the mineral when 

 heated in a closed tube. Gothite, FeoOj.HoO, and haematite are 

 probably present at times. Wherever the laterite overlies greenstone 

 an iron hydrate is the predominant constituent. 



Solutions of these laterites in a mixture of sulphuric and 

 hydrofluoric acids, prepared in a neutral atmosphere, are invariably 

 capable of reducing potassium permanganate solution, usually in two 

 distinct stages. For example, the Coolgardie laterite quoted above 

 instantaneously reduced permanganate equal to 0-80 per cent of 

 ferrous oxide, and more slowly (about 3 seconds) a further amount 

 equal to 0-54 per cent ferrous oxide. This consumption of per- 

 manganate may be due to the presence of ferrous oxide, vanadium 

 trioxide, or organic matter. jVo definite interpretation is at present 

 possible, but the writer is inclined to consider that it is in small part 

 due to the presence of a little ilmenite or magnetite, but more largely 



1 1-20 per cent at 105°. 



