468 C. J. WOODWARD ON A GKROITP OF 



Calculated into carbonates, these give 



. 



1. 



a. 



2. 



51-89 



34-62 



1-65 



12-52 



47*59 

 3474 



2-I 3 



1373 



61-34 



20-15 



3-37 



1604 





Manganous carbonate (Mn00 3 ) ... 

 Magnesic carbonate (MgC0 3 ) 



100-68 



98-19 



100-90 



No. 1 approximates in composition to a specimen of ankerite 

 from Admont, Styria, given in Bammelsberg's ' Handbuch,' and put 

 by Boficky as Ankerit «. The analysis of the Admont specimen is 

 given in column a ; and had I made but one analysis of the Lilies- 

 hall mineral, I should perhaps have felt justified in calliug it 

 ankerite. Analysis 2, however, was made from a specimen undis- 

 tinguishable in appearance from specimen 1, yet the relative pro- 

 portions of carbonates are widely different. Analysis 2 cannot be 

 made to coincide with either of Boricky's values for ankerite*. 

 The specimen, however, approximates to the formula 



3 CaC0 3 + (FeMn) C0 3 + MgC0 3J 



which requires CaC0 3 60*00 per cent., FeC0 3 23*20 per cent., and 

 MgC0 3 1 6*80 per cent., or a difference of 1*34 per cent, in the CaC0 3 , 

 0*32 per cent, in the (FeMn) C0 3 and 0*76 per cent, in the MgC0 o , 

 and would properly be described as a ferriferous dolomite. 



* Boricky (Mineralogische Mittheilungen von Tschermak, 1876, Heft i. p. 47) 

 gives the general formula for ankerite as 



(0aCO 3 +FeCO 3 )+a<CaCO 3 +MgCO 3 ), 



where x=\, 1, i, f, f, 2, 3, 4, 5, 10; so that the possible ratios of carbonates 

 are 



CaCO, =100 •>+!), 





FeC0 3 =116, 







MgC0 3 =84#. 





Putting x as |-, 1, 



4, &c, and calculating percentages, 



we have th 



possible values 









OaC0 3 . FeC0 3 . 



MgOO a 



#=£ 



48-70 37-66 



13-63 



x=l 



5000 2900 



2100 



x=i 



50-54 2516 



24-30 



#=f 



50-81 23-57 



25-62 



x=% 



51-05 22-18 



26-77 



x=2 



51-37 19-87 



28-77 



x=3 



52-09 15-10 



32-81 



#=4 



52-52 12-18 



35-30 



x=5 



52-81 10-21 



36-97 



a;=10 



53-50 



5-64 



40-85 



