■ 



On the DeweyVUe. 8 1 



15. Magnetic oxide of iron, massive and in crystals, {pnmitifoi 

 Hai'iy,) occurs in abundance near locality 7, in talc chlorite.* 



Baltimore, Feb. 1830. 



r 



On the Mineralogical and Chemical characters of the Dewci/Iite^ 

 and the probable indentity of the '^Magncsian hydrate of Silica'^ 

 with this species; by Charles U, Shepard. 



The preceding notice of the '' ^Magnesian hydrate of Silica," by 

 Mr. Tyson, agrees so well with what is known of a substance found 

 in Middlefield, Mass., that for die purpose of rendering obvious the 

 identity which I believe to exist between the two minerals, I take the 

 liberty of annexing to his IMemoir a more full account of its proper- 

 ties than has been hitlierto published. 



This mineral was discovered many years ago by Dr. E. Emmons ; 

 and is described in his Manual of IMineralogy and Geology, (Albany 

 1S26,) p. 133, under the name of ''Deweylite," in honor of Prof. 

 Dewey of Pittsfield, Mass. His description is as follows. 



"Color white, yellowish white and sometimes greenish j translu- 

 cent- Becomes slightly opaline on being immersed in water, and 

 breaks into numerous rounded fragments or coarse grains : britde : 

 easily scraped and cut with a knife, the detached fragments being pro- 

 jected w^ith considerable force. It is more or less traversed in 

 every direction, by cracks or seams, exhibiting a tendency to break into 

 short columns : decrepitates strongly before the blowpipe : becomes 

 snow white, and fuses widi difficulty into an enamel, without effer- 

 vescence : structure generally comj)act, but sometimes slightly slaty : 

 often exhibits, in the interior, mamraillary and short stalactical concre- 

 tions, which appear to be covered with the points of exceedingly mi- 

 nute crystals. It is composed principally of silex and magnesia, with 

 about thirty per cent, of water. It is found in irregular seams or 

 cavities in the brown serpentine of Middlefield, Mass. It has every 

 appearance of having been formed by infiltration." 



* Duplicate specimens of many of the foregoing minerals, as well as others here- 

 tofore noticed in the American Journal, are in the possession of myself and some of 

 my scientific friends in tliis city, which wouldbe exchanged for those of other pla- 

 ces. I am happy to say, that a mineral suppOj?ed by some to be the chabasie, and by 

 Dr. H. Hayden believed to be new, and which was mentioned in this Journal, has 

 lately been found in abundance, in large and perfect crystals, and not decomposed 

 like those formerly found. It is accompanied by beautiful pearly zeolite ; and^scme 

 farther notice of it maybe expected soon. 



Vol. XVIII— No. 1. .11 



