G. D. Hubbard — Colloids in Geologic Problems. 09 



solution must needs go beyond the clear space to find 

 sufficient concentration for the development of another 

 band. If the flowing solution remain constant in quantity 

 and condition, would not the bands maintain uniform 

 spacing instead of becoming farther and farther apart as 

 in the laboratory experiment? 



The laboratory experiment also throws light on the 

 formation of metallic copper in quartz veins; The exper- 

 imentor used a silica gel dialyzed with acetic acid I sul- 

 phuric would have served the same purpose), and mixed 

 with his gel, before it set. a solution of copper sulphate. 

 The reducing agent was placed on top. and the tiny tetra- 

 hedrons of metallic copper began to shine- in the gel. If 

 the gel was free from air or any oxidizing agent, the 

 crystals preserved their copper luster, but without due 

 precautions, they oxidized dark to black. Clusters and 

 chains of tetrahedrons formed as the process continued. 

 After many months this process produced a silica gel 

 vein with appreciable quantities of metallic copper dis- 

 seminated through it. If one wishes to repeat or extend 

 this work. Prof. Holmes 9 has given full directions for 

 preparing silicic acid gels. 



In these cases, all that is necessary to make the typical 

 mineralized quartz vein is to allow the gel to crystallize. 

 a change which has already been explained as a laboratory 

 experiment, and which seems perfectly possible as a 

 natural geologic phenomenon. 



Lhnonite seems to furnish an illustration of an ore once 

 in a colloidal state. There are six hydroxides of iron, 

 made by combining one to six molecules of water with the 

 ferric oxide, only one of which, goethite, is known in the 

 crystalline form. This is the hydroxide with one mole- 

 cule of water to one of Fe 2 3 . Clarke in the "Data of 

 Geochemistry. 7 ' p. 531, quotes Van Bemmelen as saying 

 that probably no formulas should be given to any of these 

 ferric hydroxides, but rather they should be regarded as 

 polymers of the first, or colloidal, complexes of two or 

 more polymers. Van Bemmelen in a number of papers 

 published between 1888 and 1904 so regards them, and 

 Xicolardot and Spring both consider the several hydrox- 

 ides polymers of the first. Thus the ferruginous slimes 

 in bogs and around springs, and sometimes in stalactites 



& Holmes.. H. X.. Silicite Acid Gels. Jour. Phys. Cheni., 22, 510-519, 1915. 



