CHAPTER XVI 



MECHANICAL AND CHEMICAL TESTS IN THE IDENTIFICA- 

 TION OF MINERALS AND ROCKS 



IT often happens, especially in the early years of his 

 experience, that the geologist meets with rocks which 

 none of the tests available in the field enable him satis- 

 factorily to recognise. In such cases, as already remarked, 

 he detaches one or more fresh chips of each puz/ling 

 variety, and carries them home for determination by more 

 precise processes. He may, in the first place, apply 

 some simple physical and chemical tests. Detailed 

 chemical analysis cannot of course be attempted in the 

 ordinary conditions of field-work, but much may be 

 learnt by a few easily performed experiments. 



i. Testing for Hardness. Reference has already been 

 made (p. 67) to the relative hardness of rocks as a 

 means of discriminating different kinds. This test is of 

 most value in the study of minerals ; but is not without 

 practical value in the field, as well as indoors, in the 

 investigation of rocks. The scale of hardness adopted 

 for minerals and applicable also to rocks is as 

 follows : 



