522 AUSTIN F. ROGERS 



chemical composition and physical properties than with crystalline 

 minerals. The physical properties of many of the amorphous 

 minerals can be determined as completely as those of many of the 

 massive non-cleavable isometric minerals, for in the absence of 

 cleavage and crystal form all the available properties for determina- 

 tion are scalar. 



Most authorities admit an amorphous mineral to the full rank 

 of species if it has no crystalline equivalent, but discard those with 

 crystalline equivalents. This, I believe, is inconsistent, and it 

 would seem more logical to refuse admittance to an amorphous 

 mineral until its crystalline modification is described. It is also 

 inconsistent to recognize opal and not the other amorphous equiva- 

 lent of crystallized minerals. Opal is not a definite hydrate of silica, 

 but is silica with dissolved or adsorbed water. Other amorphous 

 minerals also contain dissolved or adsorbed water and bear the 

 same relation to crystalline equivalents that opal does to quartz. 

 As shown by von Weimarn, 1 the colloidal condition is a general 

 property of matter. No one can doubt that the amorphous and 

 crystalline conditions are fundamentally different. Any given 

 substance possesses a different energy content in these two condi- 

 tions. 



If it is admitted that the properties of amorphous minerals are 

 sufficiently distinct, and we admit this when we use such names as 

 opal, pitticite, allophane, etc., we must assign the known amorphous 

 equivalents of crystallized minerals the rank of independent mineral 

 species. The first step in this direction was taken, I believe, by 

 Cornu 2 in 1909. He introduces the names kliachite, stilpnosider- 

 ite, gelvariscite, gelfischerite, geldiadochite, gelpyrophyllite, etc., 

 as names of the amorphous equivalents of hydrargillite, limonite, 

 variscite, fischerite, diadochite, and pyrophyllite, respectively. 

 This, in my opinion, is one of the important advances in systematic 

 mineralogy. Although sound from the standpoint of physical 

 chemistry, this principle has not been generally adopted. We are 

 conservative, and even desirable changes are slow in adoption, but 

 it seems strange that such names as cliachite or kliachite are not 



1 Zur Lehre von den Ziistanden der Materie (Leipzig, 1914). 



2 Zeit.f. Chem. u. Ind. d. Kolloide, IV (1909), 15. 



