114 S. L. Penjield — Mineralogical Notes. 



Art. XI V. — Mineralogical Notes ; by S. L. Penfield. 



1. Octahedrite from Magnet Cove, Arkansas. 



Up to the present time octahedrite lias been found in the 

 United States at only a few places. It is interesting, there- 

 fore, to record its occurrence at a new locality, especially as it 

 is one which is noted for the two other forms of titanic oxide, 



brookite and rutile. While exam- 

 ining the stock of minerals of Dr. 

 A. E. Foote of Philadelphia, Pa., 

 one specimen was found, among a 

 lot of brookites from Magnet Cove, 

 which attracted the writer's atten- 

 tion from its unusual crystalline 

 form. On measuring the crystals 

 they were found to be tetragonal 

 and to have the angles of octahe- 

 drite. The habit is shown in tig. 1, the forms being : 



p, 111, 1 z, 113, i x, 103, £-* 



The reflections of the signal were fairly good and the angles 

 which were measured agree very well with those calculated 

 from the length of the vertical axis as given by Miller,* 



c = i-mi. 



Measured. 

 p ~p', 111a 111 = 82° 6' 

 /ap", 111a 111 = 82 12 

 p *p {v , 111 a 111 = 43 22 



The crystals are black and have a fine metallic luster. The 

 largest are about 5 mm in axial diameter. They are implanted 

 upon a white saccharoidal albite, showing small, distinct crys- 

 tals of albite in the cavities. When tested with salt of phos- 

 phorus before the blowpipe they gave the reaction for titanium. 



Although a careful search was made, only this one specimen 

 was found, which is now in the collection of Prof. Geo. J. Brush. 

 There can be no doubt about its having come from Magnet 

 Cove, as it resembles in its character and association other 

 specimens from there and also shows a few brookite crystals. 



2. On the Crystallization of Penfieldite. 



In the September number of this Journal, 1892, page 260, 

 my friend, the late Prof. F. A. Genth, described a new min- 



* Mineralogy, 1852, p. 229. 



Calculated. 



Measured. 



Calculated 



82° 9' 



z az', 113 a 113 = 53° 54' 



z'aZ", 113 a 113 = 53 49 



54° 1' 



43 24 



z a2 !v , 113 a113 =100 20 



100 5i 



