A REVIEW OF THE AMORPHOUS MINERALS 521 



of distinct species, and of these only seventeen 1 are listed as 

 amorphous. Some of these are probably synonyms and some 

 are undoubtedly crystalline. Of the amorphous minerals 

 described since the appearance of Dana's System none has 

 been given the rank of mineral species in the appendixes of that 

 work. 



The principal reason why so few amorphous minerals are listed 

 is because the amorphous equivalents of crystalline minerals, with 

 the single exception of opal, are not recognized as distinct mineral 

 species. We find, for example, crystalline cupric oxid (tenorite) 

 united with amorphous cupric oxid (melaconite) . Amorphous 

 limonite is united with its fibrous and crystalline equivalent. 

 Crystalline and amorphous ferric oxid are both included under the 

 name hematite. 



ARE AMORPHOUS MINERALS TO BE RECOGNIZED? 



The chemical composition of most amorphous minerals is not 

 as definite as that of the average crystalline mineral, but since the 

 discovery of the variability in the composition due to solid solution 

 of such well-crystallized minerals as pyrrhotite and nephelite, we 

 can no longer insist that the term "mineral species" be confined 

 to those of definite chemical composition. Many of the amorphous 

 minerals approach closely in chemical composition the correspond- 

 ing crystalline mineral, as was first emphasized by Cornu, 2 who 

 called these minerals "pseudo-stochiolithe." Practically all the 

 amorphous minerals contain water, even if the corresponding 

 crystalline minerals are anhydrous, but this water or the excess 

 water over that present as hydrion or hydroxyl is probably not 

 essential. The myeline from Rochlitz, Saxony, for example, is 

 probably the amorphous equivalent of kaolinite, yet it contains 

 practically the same amount of water. 



Some of the amorphous minerals are definite enough to be 

 recognized, though we must, of course, allow more latitude in 



1 These are opal, collophanite, bindheimite, szmikite, deweylite, genthite, garnier- 

 ite, spadaite, saponite, glauconite, cimolite, montmorillonite, allophane, collyrite, 

 schrotterite, chloropal, and hisingerite. 



3 Zeit.f. Chem. u. Ind. d. Kolloide, IV (1909), 15, 89. 



