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ANNALS NEW YORK ACADEMY OF SCIENCES 



Constitution of Micro-aggregates. 



Those substances in particular which are apparently amorphous seem 

 to have led to the greatest misapprehension and error, which may now be 

 removed by similar treatment of their analyses. In the absence of outward 

 crystalline form they present two alternatives: they may be considered as 

 possibly either truly colloidal and optically isotropic, like obsidian; or as 

 microcrystalline but mostly homogeneous aggregates. In either case the 

 so-called "impurities" must be present. In the micro-aggregates, even 

 though one mineral may predominate, it is always safe to .presume that 

 admixture with other minerals does occur in varying but notable proportions. 

 In this respect it matters nothing whether an aggregate be macroscopic, 

 with constituents visible to the naked eye, or microscopic or even ultra- 

 microscopic; the limitations of our vision or optical instruments have no 

 bearing in any way on the settlement of homogeneity and of the question of 

 intermixture. 



It is true that in descriptions of minerals many micro-aggregates have 

 been cautiously assigned to subsidiary lists or groups, imder such headings 

 as "Chloritic minerals more or less imperfectly defined," "Magnesian 

 silicates allied to serpentine but of somewhat doubtful character," and 

 "Appendix to hydrous silicates." Yet the same pages are crowded with 

 the names of impure aggregates, figuring as minerals, mainly because amor- 

 phous and somewhat uniform in color and other characters, particularly if 

 this conclusion has been buttressed by construction of chemical ratios or 

 formulas from the analyses. 



Micro-aggregates are likely to comprise a larger number and proportion 

 of chemical components and of their combinations than those found in 

 crystals. The proposed solution of their constitution does not consist merely 

 of a calculation of the possible mineral combinations of a certain number 



