Excerpt from Tables for the Determination of Common Minerals Chiefly by Their Physical Properties: With Confirmatory Chemical Tests

The principal defects of the best tables now in use, so far, at least, as the general student is concerned, are that they have too wide a scope, embracing all or a very large proportion of the known species of minerals, and that the determinations depend almost entirely upon the chemical behavior of the species.

It is scarcely possible to overstate the enormous disparity, as regards their abundance, between the two or three hundred common minerals and the one thousand Or more rare species. The former are found abundantly in many localities, and in all good collections, and are, generally speaking, the only species the student will meet or have oc casion to identify; while the latter are very restricted in distribution, being often known from only a single locality, occuring for the most part in impure or very minute specimens, and being inadequately rep resented even in the largest and most complete collections.

The advantages of limiting determinative tables to the common spe cies are that they are then far less voluminous and complicated, the determinations can be made more readily and accurately, and the use of difficult or uncertain tests is avoided. The only disadvantage is that there must often remain the possibility that the specimen in hand belongs to one of the rare species not included in the tables. But, as already explained, this difficulty is very small; and it can not be entirely obviated by the use of the most perfect tables, since it is prob able that a large proportion, perhaps a majority, of the rare species are still unknown and unnamed.

Chemical or blowpipe tests are valuable, since the indications which they afford are usually very definite and precise and since they direct the student's attention particularly to the chemical composition and behavior of the species he is investigating, which is of great im portance. Nevertheless, there are several good reasons why they should occupy a subordinate place in a system of determinative mineralogy intended for general use. Not the least of these is their inconvenience, Since they require, in the aggregate, a considerable amount of apparatus and re-agents, in other words, a blowpipe laboratory. This consider ation, and the knowledge of chemistry which the system demands, practically restricts the instruction to high schools and colleges; and even then the chemical system is not found to be practicable in after life, when the student of mineralogy no longer has access to the facilities. Afforded by the school. Every teacher of blowpipe analysis must have noted and lamented the fact that, as a rule, the elaborate system so carefully taught is used, after the students leave school, only by the few who become professional mineralogists, chemists or miners.

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