96 W. P. Headden — Columbite and Tantalite. 



fact has been observed in regard to the stream tin, i. e. that 

 it is richer in iron than the cassiterite from the adjoining lodes. 



XVII. Yolo Mine. — digger Hill District My attention 

 was called to this occurrence of columbite by Capt. St. John, 

 owner of the property who also furnished me my best speci- 

 mens of the mineral This is different from any specimen 

 yet described. It is fine-grained, gray-black in color, and 

 the small irregular masses are penetrated by seams of mica and 

 coated with scales of the same. It is the only specimen in 

 which I have detected any admixed cassiterite. From analysis 

 XVII<2, 4*46 per cent, and from b, 4'64 per cent have been 

 deducted. The high percentage of tantalic acid indicates that 

 this mineral is rather a tantalite than a columbite ; on the 

 other hand the few small crystals obtained from this locality 

 have the form and habit of columbite and if this observation 

 is correct, the mineral should be classified as columbite. 



The three following analyses are introduced here, partly for 

 their own sake and partly for comparison. 



XYIII. Turkey Greek, near Morrison, Colorado. Specimen 

 furnished by Mr. Richard Pearce of Denver. It occurred as 

 plates packed close together and enclosed between them 

 was some pinkish feldspar, it is stained with a thin yellow 

 ochreous incrustation. 



XIX. Baddam, Conn — Specimen bought of Messrs. Geo. 

 C. English & Co., Phila. Color black, luster sub-metallic 

 rather shining, fracture sub-conchoidal with slight iridescence 

 on fracture surfaces. Easily distinguishable from the Black 

 Hills mineral. 



XX. Mitchell Co., 1ST. C— Specimen bought of Dr. A. E. 

 Foote, Phila., it resembles the Haddam mineral but is not so 

 compact. 



The first eight specimens are all from the Etta mine and are 

 arranged (p. 95) in the order of their specific gravities. It will 

 be seen that the amount of tantalate increases with the specific 

 gravity and emphasizes the fact that these various isomorphous 

 mixtures not only occur at the same locality but may even form 

 the individual members of groups of crystals. They all have 

 the habit and form of columbite, but the ratio of Cb : Ta grad- 

 ually falls from 6 : 1 to 1 : 1, and in the case of the Yolo min- 

 eral becomes 1 : 1J. If we examine the ratios afforded by the 

 two specimens of Broddbo tantalite analyzed by Professor 

 Pammelsberg we find in one case the ratio of Cb : Ta=l : 1, in 

 the other 3 : 2. Professor Dana says of the columbite from 

 Northfield, Mass., analyzed by W. J. Comstock (Appendix III, 

 page 30), " The Northfield mineral had the form and habit of 

 ordinary columbite though it is essentially a tantalite. This 

 was also true of the Branch ville (Conn.) mineral . . . ." The 



