30 Notes on the Diabase Rocks 



lating it, I have, as before, disregarded the free silica as 

 being extraneous and variable in amount. The microscopic 

 examination showed that it is to be regarded as a finely 

 crystalline form of Diabase, and the above ratio agrees well 

 with that conclusion : — 



DIABASE— MURENDEL MINE. 



Eatio. 



= 3-760 



= 1-000 

 = 1-626 



•784 





Per cent. 



Molecules. 





Si.0 2 



... 48-48 



... 161-60 1 



Acids, less 

 free Si.0 2 



A1 2 3 



... 14-57 



... 28-29 ) 

 14-60/ 



* 2 3 



Fe. 3 



... 11-68 



EeO 



2-83 



7-86) 





CaO 



... 9-56 



... 34.14 V 



RO. 



Mg.O 



... 5-55 



27-75) 





K O 



... 1-77 



3-77 

 10-74 ^ 





Na 9 O 



... 3-33 



R 2 O 



H o ~0 



... 1-72 



19-11 ( 





C0 2 



1-27 



5-78 ' 





p 2 o 5 



•45 



•63 





101-21 



Indicative Eatio = 1*194 to 1. 



Hygroscopic moisture ... "85 

 Specific gTavity ... 2*807 



This analysis may be more readily calculated for mineral 

 percentages than the former one, as being of a crystalline 

 rather than aporphyritic rock. The C0 2 and P 2 5 clearly 

 indicate the amount of calcite and apatite respectively. In 

 the absence of alterations to kaolin, serpentine, or chlorite, 

 the whole of the H 2 O probably belongs to the ferric hydrate ; 

 and the remainder of the Fe 2 3 should indicate the magne- 

 tite. In fact, there remains, however, a small portion of Fe 2 3 

 over, which may be either regarded as an analytical error, or 

 as representing ferric oxide (haematite, ironglance), which 

 has not been recognised under the microscope. The alkalis 

 may be assigned wholly to the soda and potassa felspars, 

 leaving the remainder of the Al 2 3 as before, to give the 

 amount of the lime felspar. The balance of the CaO, with 

 the whole of the Mg O, together with a proportionate part of 

 the Si 2 , should give the augite, leaving a small balance of 

 Si O 2 for the free quartz and the agate recognised under the 

 microscope. On this plan I have framed the following 

 scheme : — 



