28 Penfield and Stanley — 



a laboratory, namely the combined action of heat and pressure, 

 maintained for a considerable period of time ; conditions, 

 however, of common occurrence in natnre. Amphibole is 

 undoubtedly a mineral which commonly owes its origin to 

 what is known as pneumatolitic action, that is to aqueous 

 vapors and other gases working under the combined action of 

 heat and pressure. In minerals formed under such conditions 

 are found water with hydrogen playing the role of a metal, 

 hyclroxyl, fluorine and, as in the case of tourmaline, boron. 

 Many of the minerals have complicated chemical formulas, for 

 which possibly the mode of formation is responsible, pressure 

 and other agencies giving rise to molecular structures more 

 intricate than are generally met with. In several of these 

 pneumatolitic minerals, amphibole, tourmaline and the micas 

 for example, there may be noted the occurrence of a large 

 number of elements, of varying valences and evidently occur- 

 ring in some waj T as isomorphous constituents. 



In spite of the fact that pneumatolitic minerals have been 

 produced with difficulty, if at all, by synthetic methods, it is 

 reasonable to suppose from their common occurrence in nature 

 that they might be produced with comparative ease if the 

 right conditions could be obtained. It is probable that with a 

 suitable container provided with electric heating appliances, 

 within which a high pressure could be maintained, the condi- 

 tions favorable for the synthetic production of numerous 

 pneumatolitic minerals might be attained and satisfactory 

 results expected. 



To recapitulate, our premises are as follows : — Amphibole 

 is presumably a mineral of complex molecular structure, a salt 

 of some multiple of H„Si0 3 , very probably of an acid charac- 

 terized by a ring structure, but the number of silicon atoms 

 contained in the ring it is impossible to state. This much 

 also seems probable, that the number of silicon atoms in the 

 amphibole molecule, and their arrangement, whatever that 

 may be, exert such a controlling influence that by virtue of 

 mass effect the hydrogen atoms of the acid may be replaced 

 by elements of different valences and by radicals without 

 exerting any appreciable effect upon the crystalline form. 



Selection and preparation of materials for the new analy- 

 ses.— -The endeavor has been made to select materials repre- 

 senting a wide range in chemical composition and also with the 

 view of having the samples prepared for analyses as pure as 

 possible. Most of the specimens have been selected from the 

 Brush Collection. As a rule they were well crystallized and 

 the materials were at first carefully selected by hand picking ; 

 subsequent!} 7 they were pulverized and sifted to an uniform 

 grain, suspended in heavy solutions and from each a portion 



