1873 ] did [Genth. 



white zoisite. The University collection contains some remarkable 

 specimens. 



One forms a narrow vein of cleavable pink corundum in grayish-green 

 hornblende. Between the corundum and the hornblende is a thin lining 

 of zoisite, which becomes thicker and thicker and soon occupies the 

 whole vein, first in compact, then in cleavable columnar masses, the 

 corundum having entirely disappeared. Another piece of blueish-gray 

 corundum is on one side altered into columnar brownish-white and 

 white zoisite, whilst the interior is to a great extent changed into marga- 

 rite. Many of the other pieces show nuclei of unaltered corundum dis- 

 seminated through the mass of zoisite. 



The following were analyzed : 



a, slightly greenish-white cleavable zoisite, the result of the alteration 

 of pink corundum, by Dr. Koenig. 



b, white, slightly grayish columnar zoisite, resulting from blueish-gray 

 corundum, nuclei of which were still visible, by myself. 



c, for comparison I give the analysis of the zoisite from Unionville, by 

 G. J. Brush* (Silliman's Unionite). 



100.27 100.41 100.89 



The oxygen ratio of RO : R 2 :j : Si0 2 are as follows : 



a = 6.96 : 16.02 : 21.71 = 1 



b = 6.94 : 16.25 : 21.26 = 1 



c = 6.89 : 15.74 : 21.66 = 1 



All these analyses of the zoisite associated with corundum show a 

 slight excess of alumina, if we take the ratio of 1 : 2 : 3 as representing 

 the composition of zoisite. If this is owing to a small admixture of un- 

 altered corundum, the three specimens analyzed would contain : a 4.50 

 'per cent., b 5.0 per cent., and c 4.21 per cent, of it. 



10. Feldspars. 

 Many varieties of feldspar occur with corundum under circumstances 

 which are of the greatest scientific interest. 



a. A white, grayish and reddish variety of anorthite called indianitt 



* G.J. Brush, Sill. Jour. [2] XXVI, U9. 



