Genth.] OJU [Sep. i 9; 



By the fusion with calcic carbonate and amnionic chloride I obtained 

 11. OS per cent, of corundum ; the 2.20 per cent of corundum in Dr. 

 Koenig's analysis remained unacted upon by the fusion with sodic car- 

 bonate. 



The oxygen ratios in tliese analysis is for RO : R 2 3 : Si0 2 : H 2 0, as 

 follows : 



Genth = 0.39 : 28.32 : 19.03 : 1.58 = 1 : 72.6 : 48.8 : 4 



Koenig = (0.39) ass'd : 28.07 : 18.5G : 2.05 = 1 : 72.0 : 47.6 : 5.3. 



It will be seen that the ratio of Jl.O^ : Si0 2 is exactly = 3:2, 

 which is that of fibrolite. Although it is very probable that this variety, 

 like the two others is originally an alteration of corundum into fibrolite, 

 the latter is almost completely changed in the first two varieties and to 

 a great extent already in the third. I did not succeed in calculating from 

 the small quantities of potash, soda and magnesia any of the admixtures. 

 The 11.08 per cent, of corundum which I found, indicate the presence of 

 probably about 15 or 16 per cent, of this substance. 



18. Pakagonite. 

 A highly interesting occurrence of corundum is that at " Ochsenkopf, " 

 near Schwarzenberg, in Saxony. It is found in granular masses or isola- 

 ted grains of a blueish-gray color in a slaty rock of a brownish ash-gray 

 color. Associated with the corundum are small scales of dark green 

 chloritoid and a minute quantity of a foliated white brilliant mineral, 

 which is probably diaspore. The slaty matrix consists of very fine white 

 and brownish-white scales, and the whole appearance is so very similar 

 to that of some varieties of damourite resulting from the alteration of 

 corundum, that I considered a chemical analysis as very desirable. The 

 material for it was selected with great care and was found to have the 

 following composition : 



Si0 2 43.70 



Ti0 2 3.50 



Al,6 3 39.60 



Fe 2 3 0.66 



MgO trace. 



CaO 0.56 



Li a O trace. 



Na,0 6.52 



K,6 0.93 



Ignition 4.83 



100.30 

 The presence of titanic acid was surprising, as no rutile could be de- 

 tected with a very good magnifying glass in any of the particles. Some 

 of the slate was therefore carefully crushed without grinding and the 

 lighter particles were washed off. The heavier residue, when examined 

 under the microscope, showed numerous grains of yellowish-brown 

 rutile. 



