122 Prof. J. B. Harrison — Laterite from Quartz-free Diabase. 



These represent the passage of a normal, practically quartz-free, 

 diabase into a laterite of aluminium hydrate and iron ores, both 

 residuary and secondary, from the ferromagnesian minerals, with some 

 quartz, but without any kaolin. The finely divided quartz was 

 separated from the laterite by long-continued boiling with sulphuric 

 acid, and also by solution of the laterite in dilute hydrochloric and 

 hydrofluoric acids. The residues were examined microscopically in 

 both cases, and proved to consist only of quartz. 



The analyses when calculated to a titanium oxide constant basis 

 throw somewhat interesting light on the changes which have taken 

 place during the conversion of the diabase into laterite. The results 

 are shown in the following : — 



100-28 



41-69 



39-87 



The proximate mineralogical compositions calculated on the same 

 basis fairly well illustrate the changes in the constituent minerals of 

 the diabase during its conversion into laterite, and are as follows : — 



Quartz 

 Orthoclase 

 Plagioclase 

 Pyroxene . 

 Olivine, Serpentine, and Talc 

 Magnetite 

 Ilmenite. . 

 Haematite . 

 Limonite . 

 *Bauxite 



(Diaspore . 

 I Gibbsite . 

 * Alumina in Bauxite 



The chemical compositions of the diabase and of the outer crust or 

 laterite derived from it when calculated on a titanium oxide constant 

 basis show changes in the following constituents : — 



