Corundum from Delaware 

 Co., Pa 



Reports of Judges. 



Grains. 



1 . 49000 Black Diamond . 

 . 22021 Time, 3 minutes 



Time, 30 seconds [ 1 . 16979 Loss 



Emery, Chester, Mass f 16 . 65 



J 11 . 6968 Time, 5 minutes . 



Time, 1 minute loss. . . [ 4.9532 

 Topaz (Soute d'eau) 



Time, 1 minute loss . 

 Topaz pebble 



2.0970 



0.1263 Time, 8 minutes . 



Time, 1 minute loss. 



1.9707 



9.774 

 7.6241 



2.1499 



59 



1.2607 

 1.2235 



0.0372 



1.2235 

 1.1738 



0.0497 



1.2607 

 1.1738 



0.0869 



The emery from Chester, Mass., is composed, to some extent, of 

 magnetic iron ore. A hole was made through the specimen, leaving 

 the corundum projecting, showing that the iron was affected much 

 more rapidly than the harder material. 



A conical hole was made in the topaz pittle, which in another 

 minute would have penetrated it, had the blast been allowed to act 

 longer. The surface of the black diamond was reduced from a very- 

 rough face to almost a plane one. 



The examination of these specimens under the microscope, show 

 exactly the same characteristics as those exhibited by the rolled speci- 

 mens of the harder stones, and explain how, in nature, substances like 

 diamond and topaz may be worn away by the action of other min- 

 erals, which are even three degrees, of the scale of hardness, softer. 



These results are so remarkable as to lead me greatly to regret 

 that I did not receive your communication in time to make more 

 extended experiments, as I should like to have done, with substances 

 softer than quartz sand. I wrote to the owner of the sand-blast 

 machine, in the hope of being able to report to you an extended 

 series of investigations with different materials and softer sand. It 

 will, however, be so long before the machine will be ready to work 

 again in New York, that I have decided to report now. 



The action of this machine on the different rocks and minerals 

 will undoubtedly go a great way in explaining many difficult problems 

 in structural geology, and I have no hesitation in saying that I con- 



