366 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



those whose duties bring them into intimate relations with the subject 

 matter of a science, but so much may appropriately be said that a 

 consistent application of physical chemistry to the minerals may 

 operate in the not far distant future to develop an entirely new con- 

 ception of tiie science of mineralogy. 



As the number and scope of such exact measurements increase, 

 we gradually build up what may be called a geologic thermometer. 

 Just as the location of fossils offers a basis for estimating geologic 

 time, it often happens that a mineral takes on a variety of different 

 crystal habits, according as it happened to form at one temperature 

 or another. Quartz, for example, which is one of the commonest of 

 natural minerals and one of the most familiar, undergoes two changes 

 in its crystal form which leave an ineffaceable record. One occurs 

 at 575° and the other at 800°. An optical examination of even a 

 minute quartz fragment from the mountainside will reveal to the 

 skillful petrologist whether the crystal formed at a temperature 

 below 575°, between 575° and 800°, or above 800°. And if we could 

 have at om* disposal a great body of such exact measurements of the 

 temperature region within which particular crystals originate and 

 remain stable, we could apply that directly to terrestrial formations 

 in which this mineral occurs, and read therein the temperature which 

 must have obtained during their formation. All this will not be 

 done in the first year, and perhaps not in the first decade; but the 

 ultimate eft'ectiveness of this method of procedure in establishing 

 the relations between the minerals and the valuable ores is now as 

 certain of success as the operations of any of the sciences which have 

 now come to be cliaracterized as exact, as opposed to descriptive. 



There is one important difference between tJie great laboratory of 

 nature and its feeble human counterpart. Nature operated with 

 large masses, mixed with, a generous hand, and there was always 

 plenty of time for the growth of great individual crystals, at which 

 we marvel whenever we encounter them, and which we have some- 

 times come to regard higlily as precious stones. To carry these 

 processes into the laboratory is necessarily fraught with certain limi- 

 tations. The quantities must remam small and the time and avail- 

 able financial resources will always be limited. So long as we are 

 able to ascertain the optical character of a crystal with equal exact- 

 ness whether the crystal is of the size of the proverbial mustard seed 

 or a walnut, the scientific laboratory can not properly afford the time 

 necessary to produce the large crystals which nature offers so abun- 

 dantly. Furthermore, the crystals of nature often owe their brilliant 

 coloring to slight admixtures of impurity, which, to the scientific 

 laboratory, speU failure and are avoided with the utmost care. Most 

 of the mineral crystals, when reproduced in the laboratory, are quite 

 colorless. And so, although the question is often raised whether we 



