118 -F. A. Genth — Contributions to Mineralogy. 



Loss by ignition 0*55 



SiO„ 35-56 



T i O „ 4-58 



A1„0 3 4-43 



Fe" o 3 20-51 



FeO 1-88 



MgO 0-17 



CaO 31-90 



99-58 

 9. Allanite. 



In the hope to find among the minerals which were asso- 

 ciated with the corundum and the pseudomorphs of spinel 

 (pleonaste) after corundum, which I described in 1873 in the 

 Proc. Am. Philos. Soc, xiii, pp. 361-406 the rare tscheffkinite, 

 I examined two varieties which I had in my collection as 

 allanite ? 



a. The first variety has a velvet-black color, shows a slight 

 transparency with a greenish-black color and a vitreous luster. 

 Sp. gr. = 3 - 546. 



It is a pebble coated with white silica, resulting from partial 

 alteration. The analyzed portion was of perfectly pure ma- 

 terial (a). 



b. The second variety is of a deep brownish black color, 

 thin splinters with brownish black transparency, vitreous 

 luster. Sp. gr. = 3'491. Two small pebbles, the surface 

 slightly oxidized into a brown earthy coating. The material 

 for the analysis was quite fresh and apparently pure (b). 



a b 



Loss by ignition 2*25 2-63 



Si0 2 _* 31-67 32-04 



ThO„ 0-33 



Ti0 2 '_ 0-12 



CeO, - - ) 23 . 9g 12-91 



(LaDi) 2 O s \ 2dyb 10-24 



Y 2 3 0-36 0-33 



A1 2 3 12*20 14-02 



Fe" 2 3 4-42 7-17 



FeO. 10-89 7-52 



MnO._ 2-52 0-37 



MgO 2-08 1-47 



CaO 9-37 11-34 



100-07 100-16 



10. Lettsomite from Arizona and Utah. 



Messrs. Geo. L. English & Co. brought this rare mineral 

 from two new localities, but only one specimen has been ob- 



