1862. J ^9< [Genth. 



V. Gahrdte. 

 a. Already iu 1876, at the Centennial Exhibition, I observed, amongst 

 minerals from Western North Carolina, a specimen which was so unlike 

 any species with which I was familiar, that I was in doubt about its nature. 

 A little fragment of it which I afterwards received I put provisionally 

 under gabnite. About a year ago I recognized the same mineral again 

 amongst others which Mr. W. E. Hidden had collected in North Carolina, 

 who very kindly gave me some fragments for investigation, which proved 

 it to be gahnite. 



Apparently without form, a fracture between splinter}^ and conchoidal, 

 and of a very rich, dark green color, which can best be observed by trans- 

 mitted light. H = 7.5. Sp. Gr. = 4.576. The analysis is given below 

 (a), after deducting 0.09% SiOa and (a 2) the calculated results. 



It occurs rarely at the Deake Mica Mine, Mitchell Co., N. C. The 

 specimen at the Centennial Exhibition was about 4"=™ long and 3'''" broad 

 and, Avith an exception of thin micaceous coatings between fractures, was 

 free from admixtures ; Mr. Ilidden's specimen was about 3 to 2.5*^™ in 

 size, and was surrounded by a thin coating of about 1""" in thickness, 

 consisting of yellowish-white fine scaly muscovite, evidently the result of 

 alteration. 



b. Last summer Mr. Charles E. Hall, of the Geological Survey of 

 Pennsylvania, brought me for determination a number of specimens from 

 the Cotopaxi Mine, Chaffee county, Colorado, which were found to be 

 gahnite. 



It occurs in large rough crystals, principally octahedra, some of the 

 crystals show also the dodecahedral plane ; the largest crystal which I 

 have seen has an octahedral edge of 9*^™ in length ; the crystals are often 

 distorted and flattened out by the enlargement of two opposite octahedral 

 planes. Besides containing inclosures of galenite, and, in smaller quantity 

 of chalcopyi'ite and pyrite, they are very much altered. 



When iu a pure state it has a dark blackish-green color, and an uneven 

 to subconchoidal fracture. The material for the analysis was very carefully 

 selected, and first treated with sulphuric acid to remove the impurities, re- 

 sulting from its alteration. Mr. Harry F. Keller has analyzed it in the 

 Laboratory of the University of Pennsylvania, and obtained the results 

 (b), after deducting 1.85 per cent, of silica ; (b 1) are the results calculated 

 from the analysis : 



99.93 100.00 99.93 102.10 



