82 POPULAR SCIENCE MONTHLY. 



The "Wisconsin Geological and aSTatural History Suryej is now 

 interesting itself in the problem of the diamonds, and has under- 

 taken the task of disseminating information bearing on the sub- 

 ject to the people who reside near the " kettle moraine." "With 

 the co-operation of a number of mineralogists who reside near this 

 *' diamond belt," it offers to make examination of the supposed 

 gem stones which may be collected. 



The success of this undertaking will depend upon securing the 

 co-operation of the people of the morainal belt. Wherever gravel 

 ridges have there been opened in cuts it would be advisable to 

 look for diamonds. Children in particular, because of their keen 

 eyes and abundant leisure, should be encouraged to search for the 

 clear stones. 



The serious defect in this plan is that it trusts to inexperienced 

 persons to discover the buried diamonds which in the " rough " are 

 probably unlike anything that they have ever seen. The first re- 

 sult of the search has been the collection of large numbers of quartz 

 pebbles, which are everywhere present but which are entirely 

 valueless. There are, however, some simple ways of distinguish- 

 ing diamonds from quartz. 



Diamonds never appear in thoroughly rounded forms like ordi- 

 nary pebbles, for they are too hard to be in the least degree worn 

 by contact with their neighbors in the gravel bed. Diamonds al- 

 ways show, moreover, distinct forms of crystals, and these gener- 

 ally bear some resemblance to one of the forms figured. They are 

 never in the least degree like crystals of quartz, which are, how- 

 ever, the ones most frequently confounded with them. Most of 

 the Wisconsin diamonds have either twelve or forty-eight faces. 

 Crystals of most minerals are bounded by plane surfaces — that is to 

 say, their faces are flat — the diamond, however, is inclosed by 

 distinctly curving surfaces. 



The one property of the diamond, however, which makes it easy 

 of determination is its extraordinary hardness — greater than that 

 of any other mineral. Put in simple language, the hardness of 

 a substance may be described as its power to scratch other sub- 

 stances when drawn across them under pressure. To compare the 

 hardness of two substances we should draw a sharp point of one 

 across a surface of the other under a pressure of the fingers, and 

 note whether a permanent scratch is left. The harder substances 

 will always scratch the softer, and if both have the same hardness 

 they may be made to mutually scratch each other. Since dia- 

 mond, sapphire, and ruby are the only minerals which are harder 

 than emery they are the only ones which, when drawn across a 

 rough emery surface, will not receive a scratch. Any stone which 



