256 PROCEEDINGS OF THE ACADEMY OP [1880. 



February 28, 1818. 



On Sterlingite and Damourite. — Mr. H. C. Lewis stated that 

 an optical examination of a number of American damourites had 

 shown that they all had a large optic-axial divergence. This angle 

 was generality 72°-H°. It is an angle somewhat larger than that 

 of niuscovite, and is remarkabl}^ constant in different specimens. 

 On the other hand, the original damourite of Delesse has, accord- 

 ing to Descloiseaux, an optic-axial divergence of only 10°-12°. 

 No such angle has been found in any of the American damourites. 

 As it has been shown that damourite (" h^'dro-mica ") is an im- 

 l)ortant element in our rocks, and is of wide distribution and 

 frequent occurrence, it is essential that its characters should be 

 well known. 



The damourite of Sterling, Mass., conforming precisel}', both as 

 to composition and structure, with the t^- pe of American damourite, 

 and which Prof. Cooke has shown to have an optic-axial divergence 

 of 70° ±:, has been named by Inm, Sterlingite. This distinctive 

 name was given solely on account of its larger optic angle. But 

 it appears that this large angle is characteristic of all American 

 damourites, and probably of many European ones.^ It therefore 

 follows either that all of our damourites should be called Sterlingite, 

 or that the name should be dropped ; there would otherwise be 

 confusion. Notwithstanding the exceptional optical character of 

 the mineral examined by Descloiseaux, it is thought that identity 

 of chemical composition and of physical properties is sufficient 

 reason for retaining the original name of Damourite. 



March 25, 1878. 



Vanadium in Philadelphia Bocks. — Mr. Lewis said that he had 

 discovered the presence of Vanadium in hornblendic gneiss near 

 Wayne Station, Germantown. The presence of sphene in that 

 rock suggested the search for vanadium, recent researches having 

 shown that this element frequently accompanies titanium. The 

 following method was employed for its detection. The pul- 

 verized rock was slowlj' heated in a crucible with sodic carbonate 

 and sulphur. After partial fusion the mass was digested in warm 

 water and the filtrate acidified. The precipitate was washed, ignited, 

 and fused with sodic carbonate and sodic nitrate. It was now 

 digested in water, filtered, the filtrate concentrated, and solid 

 ammonic chloride added. A precipitate fell, which was found 

 by blowpipe and other tests to contain pure vanadium. An 

 exfoliating hydrous mica occurred at this locality, resulting 



^ V. " The optical characters of some Micas :" by 11. C. Lewis, Proc. 

 Min. and Geol. Section, October 22, 1877. 



