Rocks of Noyang. 



27 



very little more than a trace of free ores of iron in this 

 example. Subjoined is the quantitative analysis : — 



No. 2. — Chloritoid. 





Per cent. 



moiecmar 

 Proportions. 



Eatio. 





Si0 2 .. 



. 34-39 



.. 1-146 SiO a 



... 1-146 . 



. 1-7 



A1 2 3 . 

 Fe 2 3 . 



. 24-38 

 . 14-17 



... -473 \ p n 

 ... •177/ R ^°3 



... -650 . 



. 1- 



FeO . 



1-81 



... -050) 







CaO 



. 3-80 



... -135 VKO 



... -735 . 



.. 1-1 



MgO 



. 11-01 



... -550 j 







K o 



1-64 



... -035) 



... -030VR 



... -702 j 







Na 2 . 



•95 



... -767 . 



. 1-2 



H 2 . 



. 6-32 









98-47 









Hygroscoj 



ic moisture, 



1-20 c 212° F. 







Unless it were possible to isolate the impurities and to 

 separate and examine each of the two component minerals, 

 no certain conclusions could be drawn as to the real nature 

 of the latter ; but it may be possible by calculating the 

 percentage to arrive at an approximation to the truth. 

 The constitution of the rock from which the sample was 

 extracted renders itmost improbable that the impurities can be 

 anything else than felspar and quartz; the examination which 

 I have made of the Noyang igneous rocks renders it further 

 most probable that the felspar is albite or an oligoclase very 

 near to it. Thus the impurities may be calculated out, and 

 the remaining molecular proportions should give the consti- 

 tution of the mixed chloritic minerals. On this basis I have 

 made the subjoined calculation. It raises a strong presump- 

 tion that the mineral is a mixture of two of the chlorite 

 group, one having the constitution of chlorite and the other 

 of chloritoid. Under the microscope the former is colourless 

 or white, and therefore probably free from iron ; the whole 

 of the iron therefore goes to form the latter. 



d 2 



