W. T. Schaller — Ludwigitefrom Montana. 149 



in isomorphous mixture with the corresponding ferrous ferric 

 magnesian borate, to the extent of 57 per cent or over half. 

 If some of the ferrous iron present in the sample belongs to 

 the forsterite or the carbonate, the percentage of the magnesian 

 borate would be still greater. 



Ludwigite from Hungary. 



For comparison with the above, an analysis was also made 

 of the ludwigite from Hungary. The quantitative analysis, 

 made on the nnely radiating black mineral, is as follows : 



Analysis of ludwigite from Hungary. 



12 3 Average 



FeO ".. 15-84 15-68 15-80 J5-84 



MgO - 28-88 28-88 28-88 



Total iron as Fe,0, . . 53-35 52-74 5372 



Fe^, .- 35-67 



H,0— -50 -52 -51 



H,0 + -78 -86 .... -82 



CO, -90 -90 



Insol -32 -40 -36 



BA [17-02] [lV-02 ] 



100-00 



The ratios from the average analysis give, after deducting 

 sufficient MgO for the CO, to form magnesite, the formula 

 FeO.Fe.Og.SMgO.B.O,, as shown below. 



Ratios of ludwigite analysis. 



FeO -220 -99 



MgO -702 3-06 



Fe.O, -223 1-00 



B.O, -243 1-09 



CO,--. --- -020 



Summary. 



The isomorphous relation of the FeO and MgO in ludwigite 

 can be well shown by bringing together the available analyses, 

 which also shows how closely the mineral from Hungary agrees 

 with the calculated values for the pure ferrous-iron ferric 

 magnesian borate. The first column gives the calculated values 

 for FeO.Fe,03.3MgO.B,03, the second, third, fourth, and fifth 

 the analyses of the Hungarian mineral and the sixth that of 

 ludwigite from Montana. 



