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 1s 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 shghtest 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 lke 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 mineralogical 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 
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