550 



Wright — Three Contact Minerals. 



which case spurrite is triclhric instead of monoclinic ; the rela- 

 tions of the optic properties for different wave-lengths are then 



Fig. 



Fig. 2. — Etch figures on good cleavage face of spurrite produced by 10 sec. 

 immersion in cold 5 per cent HC1. Magnification 150 diameters. 



Si0 2 26-96 



TiO„ -01 



Al a O, '39 



Fe 2 3 ) 



FeO \ Li 



MnO -03 



MgO -23 



CaO 62-34 



Na 2 -05 



K 2 trace 



H 2 none 



CO„ 9-73 



la 

 •4467 

 •0001 

 •0038 



•0007^ 



•0004 



•0058 



1-1114 



•0008 



•2212 



99-85 1-7909 



Calculated as Fe 2 3 . 



2 

 27-13 



62-98 



9-89 



100-00 





1. Spurrite, Velardena, Durango, Mexico, E. T. Allen analyst. 

 la. Molecular proportions of 1. 



2. Theoretical percentage weight conrposition for the formula 



2Ca Q Si0 4 .CaCO,. 



2 4 3 



