Kip — Determination of the Hardness of Minerals. 23 



Art. III. — A New Method for the Determination of the 

 Hardness of Minerals ; by H. Z. Kip. 



1. The hardness of minerals is perhaps their most obvious 

 physical characteristic. It was natural, therefore, that no sooner 

 had minerals become an object of scientific inquiry than efforts 

 were made to determine the relative, and later the actual hard- 

 ness of various species. Simple as the problem would appear 

 at first glance, the results for the mineralogist of more than a 

 century of intermittent investigation, carried on by more than 

 a score.of different investigators, are surprisingly meager. Every 

 text-book of mineralogy gives, it is true, a rough statement for 

 the mean relative hardness of each species described, as referred 

 to an empirical scale of ten grades (Mohs's scale), and for 

 ordinary determinative purposes this is valuable, though less so 

 than it might become. We know also in a general way that many 

 minerals show greater hardness on one crystal face than on 

 others, though specific information is lacking for the most part 

 in the manuals. Differences have also been shown to exist on 

 one and the same face according to the direction of the test. 

 The curves obtained by plotting these different values reveal a 

 direct relation to the symmetry of the crystal and form the 

 most important result yet attained in the study of hardness, 

 though comparatively few minerals have been investigated and 

 the curves established by different investigators are far from 

 uniform. 



The main problem, however, that has engaged attention, the 

 determination of numerical values for every degree of hardness, 

 has as yet found no satisfactory answer. Several experimenters 

 have, it is true, arrived at values for 8, 9 or even all 10 of the 

 members of Mohs's scale, but these results vary so greatly 

 among themselves that without some method of control or 

 verification it is impossible to place confidence in any of them. 

 Thus Iddings's Rock Minerals, to quote one of the most recent 

 publications, allows us to believe with one authority that the 

 hardness of gypsum as compared with corundum (assumed to 

 be 1000) is "04, or with another that it is 1"25, more than 30 

 times as great, or with a third that it is 12 # 03, 300 times as 

 great. 



2. Corresponding to the lack of uniformity of result, and 

 indeed largely responsible for it, we find varying conceptions 

 as to what hardness really is and of the factors upon which it 

 depends, no agreement as to what method, theoretically or 

 practically, would give the most reliable returns, the assumption 

 of various unproved conditions, the confusion of physical with 



