W. P. Headden — Columhite and Tantalite. 101 



but did not exceed two feet. The columbite was found at only 

 one point : the underside of the granite is here very even and 

 smooth and consists, for about two inches, wholly of mica 

 crystals whose cleavage planes stand at right-angles to the wall. 

 The inner edge of this band of mica is also sharply defined 

 but irregular. The outer surface, that is the under surface as 

 the granite lies, is filled with minute crystals of columbite 

 lying in all directions as though a crop of small crystals had 

 separated first, forming a swarm of them which adhered to 

 the wall and the larger crystals seem to be extensions of these 

 points into- the mass ; only a few points, however, have developed 

 into larger crystals. If there were two periods of growth, this 

 would account for the peculiar pointed appendages to many of 

 the crystals. Many of these crystals are short, doubly ter- 

 minated but much distorted, and attached at the side as the 

 more perfect ones indicate. 



The band of mica varies in thickness up to two inches and 

 seldom incloses any other mineral than the columbite ; the 

 quartz and feldspar, (mono- and triclinic) rest upon the mica 

 while an occasional beryl penetrates its mass. The columbite 

 crystals do not enter the beryl as they do in the Etta mine, but 

 are sometimes found in the feldspar, immediately adjacent to 

 the mica, they are often rusty, and some of them thickly coated 

 with oxide of iron, and the most of them are not at all or only 

 faintly striated. 



The crystals have a habit often observed in ordinary colum- 

 bite, and such approximate angles as can be obtained corre- 

 spond with those usually accepted. The planes present are : 

 100, 001, 010, 110, 530', 133, 021. The development of the 

 prisms 530, 110, especially the former, gives the crystals a flat- 

 tened form in the direction of the macrodiagonal axis. 



I. One of the largest crystals, weighing one and a half grams, 

 was used for this analysis ; the crystal was rusty, and had to be 

 cleaned by boiling in dilute hydrochloric acid, its color after 

 cleaning was black, luster sub-metallic, a little shining, fracture 

 uneven, streak brown, powder grayish brown. Specific gravity 

 = 6*170. II. Three small crystals, specific gravity not deter- 

 mined. The analyses are as follows : 



I. II. 



Sp. grav. = 6* 1 70. Sp. grav. undetermined. 



At. equiv. At. ratio. At. equiv. At. ratio. 



Cb 2 5 47-22 35-25) 45-66 34-07) 



Ta 2 5 34-27 15-44 [ 5090 2-07 35'53 ■ 1600 [• 50-32 2-01 



Sn0 2 -32 -21 ) -38 -25 ) 



FeO V89 2-62) L . 2-29 3"04 i 



MnO 16-25 21-97 \ l ^ 0y L 16-25 21*4-7 V 



99-98 100-00 



Ratio Cb : Ta = 7 : 3, Fe : Mn == 2 : 17. 



