106 CLASSIFICATION OF MINEBALS. 



glass be transparent, or filled with air-bubbles ; coloured or 

 colourless ; homogeneous or heterogeneous ; and whether 

 the enamel be smooth, or have the appearance of a frit, or 

 whether it be homogeneous or heterogeneous. 



A fragment of the mineral well roasted, to drive oif all 

 metallic matters, is then to be heated with the different 

 fluxes, and the results noted, observing all the particulars 

 above enumerated. The order in which the different appear- 

 ances take place must likewise be noticed, and whether 

 they occur on the first application of heat, or after a long 

 exposure to its action. For earthy minerals, charcoal is 

 not a convenient support ; they may be first dried in the 

 matrass ; and then a small scale held in the forceps is to be 

 heated, first in the outer flame, then in the inner, in order 

 to try its fusibility. If it should prove refractory after a 

 long application of the inner flame, and if no appearance of 

 roundness on the point or edges of a minute scale or splinter 

 can be discovered through a lens, it may be considered 

 infusible by itself, and may then be heated with soda, on 

 platinum foil, or wire. By this process, fusion will be 

 effected, and the tinge imparted to the glass thus produced 

 will indicate the metallic oxide, which forms the colouring 

 matter of the mineral. 



CLASSIFICATION OF MINEKALS. Mr. Griffin divides mine- 

 rals into four classes, according to the phenomena which 

 they present when exposed to the action of the blowpipe, 

 and other characters easily ascertained. 



The classes comprise 



1 Combustible minerals. 



2 Metallic minerals. 



3 Earthy minerals. 



4 Saline minerals. 



1." The combustible minerals are distinguished by the 

 following characteristics. 



They are of low specific gravity, generally below 2'0, water 

 being as I/O ; none, with the exception of the diamond, being 

 above 2 '5, and some so light as to float on water. 



They are all (with the exception of the diamond) soft, 

 yielding easily to the knife ; some are liquid. 



Some of them are highly combustible, at or below a red heat. 

 The rest are all, more or less, combustible by the action of 

 the blowpipe ; even the diamond is slowly combustible at a 

 less heat than is required to melt silver 



