396 Miscellanies. 



to a publication ; but the truth is that I had discovered the mineral sev- 

 eral months previously, and had distributed nearly all my specimens 

 among my friends. My whole paper was published in the Society's 

 Journal, Vol. 4, page 35, under the date of the Qth Aprils 1841. Prof. 

 Hitchcock's report was only published the following November. These 

 facts amply justify the statement in the excellent mineralogical volumes 

 of Messrs. Alger and Dana. 



With reference to Prof. Shepard's charge in the same communica- 

 tion, that I have been unjustly harsh to him in my remarks on Pyro- 

 chlore, I need make no reply to those who have read the controversy. 



In the case of pyrochlore in question, he seems to have narrowed the 

 claim of distinction between this mineral and his microlite, to the single 

 character of specific gravity, the first being 4-2, the second 5-5, which 

 difference he is unable to reconcile. Probably this arises from his hav- 

 ing seen so few crystals of this rare mineral from Chesterfield. After 

 having supplied Mr. A. A. Hayes with ohonXjifteen grains for his analy- 

 ses, and distributed specimens to most of my friends here and in Europe, 

 I have still left more than five or six times as many crystals as he avers 

 to have seen. 



In these the eye alone can discover considerable diversity in com- 

 position, the texture varying from sub-granular to the vitreous character 

 of those from the Swedish localities ; the external layers of some are 

 translucent yellow, the internal parts being a dark brownish black, and 

 vice versa ; others are from a red brick color to a transparent yellow — 

 all agreeing in form. 



Pyrochlore is essentially a columbate of lime ; but the specific grav- 

 ity of specimens from different, nay even from the same localities, 

 must vary, as it is mixed with varying quantities of accidental and 

 different ingredients ; that from Fredericksvarn, according to the elab- 

 orate analysis of Mr. Hayes, containing besides columbic, chiefly titanic 

 acid. All columbic minerals are of a higher specific gravity than titanic 

 and the other accidental mixtures of pyrochlore, columbite rising as 

 high as 6-1, while anatase, a pure oxide of titanium, is as low as 3"8. 

 The Chesterfield pyrochlore, specific gravity 5-4, contains nearly 80 

 per cent, columbic acid, (A. A. Hayes,) while that from Sweden, ac- 

 cording to the same authority, specific gravity 4-2 contains only 53 per 

 cent, columbic and 20 per cent, titanic acids. This is alone sufficient 

 to account for the difference in the specific gravity of the mineral from 

 each locality ; but there are several other considerations both chemical 

 and crystallographic, on which I will not dilate now, that render this 

 character of little value in mixed minerals. 



If Prof. Shepard, however, following up the discovery of columbate 

 of lime, will proceed to ascertain its true composition and specific 



