E. S. Dana—SamarsMte of Mitchell County, K C. 203 



/a 7=122° 46', 7^^=151° 23' (152°), w^ 1=110° 36' (110°), 

 i-i^ 1=130° 7', 7^ 1 = 137° 14', i-%^ 3-|=125°55'(126°), /-^^ 3f = 

 135° 46' (136°). 



The position here adopted shows most favorably the probable 

 relation of the samarskite, of North Carolina, to the crystals 

 of yttrotantalite described by Nordenskitild. 



Samarskite (Dana). Yttrotantalite (Nordenskiold). Columbite. 



7a 7 122° 46' 123° 10' (122M8',/-|) 



^■-2A^■-2 95° 94° 32' (94°58',\-n 



l-^Al^ 93° (87° 24', fi) 90° 15' 



H Afr (101° 24') (101° 62') 101° 26' (7) 



The parentheses indicate that the forms referred to have not 

 been observed. The pyramidal planes of samarskite (1 and 

 3-f ) are not known on yttrotantalite. It will be observed that 

 while in the prismatic zone the agreement between the two 

 species is close, in the domes the variation is considerable. 



The prism of samarskite referred to the axes of columbite 

 (Dana's Min., p. 516) is z-|, and on this basis the other planes 

 become as follows: ^2=^■-J, 1 = 1-|, 3-|=2, 1-1=1-1. 



The crystalline form of euxenite has not been very clearly 

 made out, but it seems to be closely related to that of sa- 

 marskite ; for 7^ 7, Dahl gives 126°, Greg 120° ? (122° 46' 

 samarskite); i-tysm-l^lb^ and 153°, but i4A2-t=152° 13' 

 (samarskite) ; also two pyramids are mentioned giving the 

 angjesa^^> =107(^^1 = 110° 85' samarskite), i-l^p^=U&'' 

 (135° 46' samarskite). 



The method of association of crystals of samarskite and 

 columbite at Miask (to be mentioned later) seems to suggest 

 that the broad plane, i-i of the figure, may possibly correspond 

 to the plane i-% of columbite. (To avoid confusion it must be 

 noticed that ^-^ columbite, Dana's Mineralogy = ^■-^ Naumann, 

 and 7 Dana = i-s Naumann.) This idea is supported by a sin- 

 gle one of the specimens under examination, where of two asso- 

 ciated crystals, the cleavage plane (probably i-i) of the colum- 

 bite was exactly parallel with the plane of the samarskite called 

 t-i above. If now this change is made, the planes, before men- 

 tioned, become as follows: If i-^2=I and i-l=i-l then I=i-\ 

 1=1-2, 3-f = 2-|. The consideration of all the facts, however, 

 seems to show that the method first proposed should be adopted. 



It may also be mentioned here that several of the minerals of 

 this group show angles of 91°-95°, 128^ etc., in the prismatic 

 zone, although in the other zones there is no apparent corre- 

 spondence, and the habit is quite different 



The occurrence of two other minerals of this tantalic group 

 has already been mentioned. One of these minerals occurs in 

 regular octahedrons, sometimes nearly an inch across, with the 



