380 DETERMINATION OF MINERALS. 



Taste is of limited value, as few minerals are sufficiently 

 soluble ; but among soluble minerals it is easily observed, 

 and often decisive. 



Action of acids, cold or hot, in trials as to effervescence, 

 solubility, gelatinizing or not, and in making solutions for 

 examination with other reagents, is a very important means 

 of distinguishing species. 



Blowpipe reactions are easily obtained, and of the high- 

 est value. 



Specific gravity is an important reliance. 



Refraction and polarization afford valuable criteria for 

 distinguishing species, and in a few cases no other means 

 are so reliable short of chemical analysis. 



The following hints may be of service to the beginner in 

 the science, by enabling him to overcome a difficulty in the 

 outset, arising from the various forms and appearance of the 

 minerals quartz and limestone. Quartz occurs of nearly 

 every color, and of various degrees of glassy lustre to a dull 

 stone without the slightest glistening. The common gray- 

 ish cobble-stones of the fields are usually quartz, and others 

 are dull red and brown ; from* these there are gradual transi- 

 tions to the pellucid quartz crystal that looks like the best 

 of glass. Sandstones and freestones are often wholly quartz, 

 and the seashore sands are mostly of the same material. It 

 is therefore probable that this mineral will be often en- 

 countered in mineral ogical rambles. Let the first trial of 

 specimens obtained be made with a file, or the point of a 

 knife, or some other means of trying the hardness ; if the 

 file makes no impression, there is reason to suspect the 

 mineral to be quartz ; and if on breaking it, no regular 

 structure or cleavage plane is observed, but it breaks in all 

 directions with a similar surface and a more or less vitreous 

 lustre, the probability is much strengthened that this con- 

 clusion is correct. The blowpipe may next be used ; and 

 if there is no fusion produced by it in a careful trial there 

 can be little doubt that the specimen is in fact quartz. 



Calcite (calcium carbonate), including limestone, is an- 

 other very common species. If the mineral collected is 

 rather easily impressible with a file, it may be of this spe- 

 cies ; if it effervesces freely when placed in a test-tube con- 

 taining dilute hydrochloric acid, and is finally dissolved, the 

 probability of its being carbonate of lime is increased ; if 



