MINERALS 255 
easily be scraped away, whereas the Quartz will be 
scratched only with difficulty. 
The hardness of a mineral may be tested by rubbing 
the specimen over a file and noting the amount of fine 
powder and noise produced in the process. The softer 
the mineral is, the greater will be the amount of 
powder and the less the degree of noise. 
A scale of relative hardness should be made out— 
indeed found out—before applying this test. Such a 
scale as that given in books on mineralogy is 
beyond the scope of the enquiry primary school 
children could be expected to undertake. A few of 
the minerals most easily obtained should, however, be 
operated on and arranged ina scale of hardness, which 
would serve as a basis of comparison when other 
specimens were being tested. Rock-salt, Calcite, Fel- 
spar, Quartz, are suitable minerals for such a scale. 
In this connection, too, comparisons and contrasts 
are useful exercises. On being asked which is the 
harder—Glass or Iron—most children will answer “the 
latter,” and, moreover, they will give as a reason for 
their opinion, that Glass is more easily broken than 
Iron. It is only after a good deal of questioning they 
are brought to see that brittleness and hardness are 
different properties, and that a simple way of deter- 
mining the latter in the case of any two substances, 
is to scratch or endeavour to scratch one with the 
other. 
Form.—Whether crystalline or non-crystalline, It is 
not at all advisable to make the examination of 
minerals too complicated; hence teachers will do 
well to omit all consideration of the many terms that 
are employed under the head of form, and to confine 
the investigation here to the general shape of the 
