Sep. 19. 1873.] 'JUl [Genth. 



CONTRIBUTIONS FROM THE LABORATORY OF THE UNIVER- 

 SITY OF PENNSYLVANIA. 



NO. I. 



CORUNDUM, 

 Its Alterations and Associated Minerals. 



(Bead before the American Philosophical Society, September lQt/t, 1873.) 

 By F. A. Genth. 



At the meeting of the American Philosophical Society of April 21st, 

 1871, I have exhibited and described several peculiar crystals of corun- 

 dum, either "wholly or partly altered into other mineral species. The 

 chemical examination of these and many others, which I have since re- 

 ceived, has given results and led to conclusions which, in connection 

 with their paragenesis, are of not less interest to the chemist and mine- 

 ralogist than to the geologist. 



My information as to tbe occurrences of corundum in Europe and Asia 

 is too limited to give a full outline of the same ; I shall confine myself 

 therefore, to those of this country and shall endeavor to give briefly the 

 most striking geological features under which they have been observed. 



Tbe rocks of the Laurentian System contain but very little corundum, 

 and only a few isolated crystals of white, red and blue colors have been 

 found in the granular limestones belonging to this formation. It occurs, 

 for example, associated with spinel, chondrodite, hornblende, graphite 

 and numerous other minerals at Warwick and Amity, in the State of 

 New York ; at Newton, Vernon and Franklin in New Jersey. 



The largest deposits of corundum known in the world, occur in the 

 chromiferous serpentine or chrysolite formation, and in the rocks imme" 

 diately adjoining the same. Numerous localities have been developed 

 from Massachusetts to Alabama, and it will always be a very interesting 

 question, by what agencies such enormous quantities of alumina could 

 have been precipitated to form corundum, which, by its subsequent 

 alteration has given rise to many of our most widely distributed minerals 

 and rocks. 



The most important corundum deposit in the Eastern States has been 



discovered by C. T. Jackson,* at Chester, Mass. ; it was subsequently 



described by C. U. Shepardf and J. L. Smitb4 



' It consists of crystalline corundum in a fine scaly chlorite, or of a 



peculiar mixture of granular and crystallized corundum wi th magnetite 



(which is generally titaniferous), intermixed with more or less of a 



chloritic mineral. The whole deposit traverses two mountains for about 



four miles, with an average thickness of four feet, and lies in a talcose 



slate and serpentine between gneiss and mica slate, iu the centre of the 



*C. F. Jackson, Sill. Journ. [2] XXXIX. 88. 



tC. U. Shepard— Sill. Journ. [2] XL. 112-123; XLII. 421; XLVI, 256. 



; J. L. Smith— Sill, Journ. [2] XLII, S3. 



A. P. S. — VOL. XIII. 2T 



