THE USE OF THE ELECTROMAGNET IN 



PETROGRAPHY 



By T. CROOK, A.R.C.Sc.L, F.G.S. 

 Scientific and Technical Department, Imperial Institute 



PAGE 



i. Introduction 30 



2. Historical Review 3! 



3. Apparatus Required 43 



4. Preparation of Material 46 



5. Separation of the Minerals 46 



6. Conclusion 50 



1. Introduction 



It is well known that minerals exhibit varying degrees of 

 permeability in a magnetic field, in consequence of which 

 grains of one mineral can often be separated from those of 

 others. In recent years the method of magnetic separation 

 has become very important in the mining world. It is quite 

 indispensable in a large number of ore-dressing operations, 

 in which domain its utility is fully recognised. 



In the laboratory also, this method has often been used with 

 great advantage, more especially in the isolation of minerals 

 for chemical analysis. Indeed, the magnet, and especially the 

 electromagnet, must be regarded as a very useful piece of 

 petrographical apparatus. Experience has shown that it is 

 capable of extensive use qualitatively, while in special cases 

 it yields quantitative results which are fairly accurate, particu- 

 larly in the examination of sands. 



Considering the ready and extensive applicability of this 

 method in rock studies, there is scope for surprise that it has 

 not been more widely adopted, for there can be little doubt 

 that, among geologists, the practical utility of the method is 

 much undervalued where not completely ignored. This may 

 be due in some measure to unfamiliarity with the results already 

 achieved. Hence it is proposed in this article to give an 



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