GEOPHYSICAL LABORATORY.* 



Arthur L. Day, Director. 



In studying the minerals which participate in rock formation, we 

 should bear in mind always that the main purpose of such studies is 

 not merely to add to the list of known compounds whose elementary 

 properties have been measured, but rather to learn the important 

 characteristics of the component members of a great number of systems 

 of mineral mixtures which we call the natural rocks. A knowledge 

 of the characteristics and relations of these component minerals pro- 

 vides the only possible approach to a competent knowledge of the 

 manner of formation of the earth. We are not able as yet to follow 

 Nature in her full complexity; in fact, we know at the moment very 

 little of the conditions of formation or of the relations of the minerals in 

 the more conunon igneous rocks. Recognizing this fact, we turn from 

 the complex rocks to the simpler component minerals, and finding 

 these in turn complicated by the admixture of other minerals and of 

 volatile matter, the relations of which we can not for the moment solve, 

 we turn finally to chemically pure minerals, prepared and crystallized 

 in the laboratory, upon which we seek to establish the foundations of 

 the system of knowledge which will one day result from such studies. 



Pursuing this plan, the first task to which a laboratory dedicated to 

 the study of this problem must address itself is the preparation of min- 

 eral types representing the individual components from which rocks are 

 made. It is necessary to make these in the laboratory, because they 

 are almost never found in nature entirely free from admixtures of small 

 quantities of other minerals which behave like impurities and serve to 

 veil the characteristic properties of these primary ingredients. When 

 it was found practicable to prepare these mineral types in a state of 

 high chemical purity, the first step in an exact science of the mineral 

 relations was taken. The thermal and optical properties of these 

 primary components could then be studied at leisure; the conditions 

 for their absolute identification could be established; their individual 

 stability in the various conditions of rock formation fixed, and the 

 characteristic properties which they exhibit in their relations with other 

 minerals determined. 



Following upon this segregation of the primary components in rock 

 formation, and the determination of their characteristic properties, 

 both physical and chemical, the investigation proceeds with construc- 

 tive sequence to discover the relations between two such components 

 when mixed together in all proportions and under measured conditions 

 (temperature, pressure, surrounding atmosphere, etc.) corresponding 



♦Situated in Washington, D. C. (For previous reports see Year Books Nos. 3-12.) 

 134 



