HOLLAND : PECULIAR FORM OF ALTERED PERIDOTITE 



The Breunnerite phenocrysts. 



The phenocrysts which have been referred to as breunnerite 

 contain numerous inclusions of magnetite-dust, talc and picrolite, all 

 of which can be distinguished from the pure mineral by chemical 

 analysis. 



A piece of the mineral, having a specific gravity of 3*168, was 

 selected for analysis, and gave the following results : — 



Insoluble residue 



. 1-57 



Lime .... 



. trace 



Magnesia . 



• 39' 2 ° 



Ferrous oxide 



. 8-27 



Ferric oxide 



• 2-93 



Carbonic acid 



. 47-oi 





98-98 



This is equivalent to — 





Talc and picrolite 



. i'6 



Magnesium carbonate . 



. 827 



Ferrous carbonate 



• u-3 



Magnetite . 



. 4-4 



IOO'O 



The molecular ratio of MgC0 3 to FeC0 3 is thus 10 : I, which is 

 the ratio existing in the variety of these mixed carbonates to which 

 Haidinger in 1825 gave the name breunnerite. 1 



The Matrix. 



For an examination of the matrix, fragments having a specific 



gravity of 2-853 were crushed and analysed, with the following 



results : — 



Silica ....... 42-20 



Iron oxide ( calculated as Fe 3 4 ) 3 . . i3'59 



Magnesia ....... 30-41 



Carbonic acid 



Water 



Sulphur 



5'3° 

 773 

 on 



99'34 



1 Mohs' Treatise on Mineralogy, 1825, I, p. 411. 



3 Distinct reactions were obtained for chromium ; but the quantity was 

 not estimated. 



( 4 ) 



