26 Penfield and Stanley — 



no means of determining the size of the molecule of a crystal- 

 lized solid. Metasilicates are naturally and readily written 

 structurally as ring ^formulas, and although such formulas are 

 wholly hypothetical they are at least suggestive and hence use- 

 ful. If H g Si 4 12 is the formula of the amphibole acid, or per- 

 haps H 16 Si 8 24 , natural ways of expressing these graphically 

 would be as follows : 



H— (\ /O— H H— N H "°\ / 0_H y O— H 



\Si_0— Si< \Si_0— Si— O— Si< 



H— <\ " v yO—H H— (\ V y /O— FI 



\Si— O— bi< >Si Si< 



H— CK \0— II II— O/i ' \0— H 



H-0 V V 0-H 



\Si_0— Si— O— Si< 



H ~ 0/ H-0/ Vtl X °- H 



Although wholly incapable of proof, it is altogether within 

 the bounds of reason to believe that the amphibole acid has a 

 ring structure, and that as in organic chemistry we have a 

 benzol ring which plays so important a role in a vast number 

 of compounds, so in mineral chemistry we may speak of a prob- 

 able am/phihole ring, carrying with it a certain controlling force 

 which conditions a kind of crystallization recognized as char- 

 acteristic for the amphibole group of minerals. As will be 

 pointed out later, calcium atoms replace one quarter of the 

 hydrogen of the amphibole acid, and it may be that the posi- 

 tion of the particular hydrogen atoms replaced by calcium is a 

 matter of importance, just as in organic chemistry the ortho-, 

 meta- or para-positions in the benzol ring are determining fac- 

 tors. 



As has already been stated, it is believed that amphibole 

 has a complex molecular structure ; it is not readily made 

 artificial!} 7 and if fused and allowed to cool there result simple 

 substances, especially pyroxene. If the ring theory is correct, 

 it may be assumed that by fusion the amphibole ring is broken 

 down and is incapable of reformation under ordinary condi- 

 tions of heat and pressure. 



To our knowledge amphibole has only once been made arti- 

 ficially, and this result was achieved by von ChrustchofE.^ 

 The accomplishment of this brilliant and too little known 

 experiment is so important and throws so much light upon the 



*Neues Jahrbuch 1891, 2, page 86. [In a recent article entitled, "Min- 

 erals of the Composition MgSi0 3 ; Case of Tetramorphism " (this Journal, 

 Nov. 1906), Messrs. E. T. Allen, F. E. Wright and J. K. Clement have de- 

 scribed the synthesis of orthorhombic and monoclinic forms of pyroxene and 

 amphibole. The monoclinic amphibole was obtained with considerable dif- 

 ficulty and only in small amounts and in microscopic crystals. W. E. Ford.] 



