Mineral Syn/ficsis. 163. 



phous agenc^^ In the pyroxenes, for example, magnesian 

 protoxide of lime and iron figured, and mineralogists gave 

 special names to these types ; as, diopside, augite, which 

 were characterized by a certain base united with silica. The 

 v^arieties furnished by nature differed from the theoretical 

 ones in chemical composition, values of the dihedral angles, 

 position and value of axes of optical elasticity. Synthesis 

 alone furnished the theoretical types and gave the exact phys- 

 ical measurements. 



4 Mineral synthesis determines the individuals belonging 

 to a family, and discovers the true isomorphism of the 

 series in question. The family of the spinels is composed 

 of many members, which pass from one to the other by 

 isomorphous means, as demonstrated chemically by Ebelmen. 

 Inversely the artificial reproduction of the feldspar series 

 proved the individuality of oligoclase and labradorite, and the 

 isomorphism of albite and anorthite, with a possibility of a 

 mixture of the two in all proportions. One was formed with 

 a composition between oligoclase and labradorite, showing 

 two series of microlites, one showing longitudinally as nat- 

 ural oligoclase, the other, with a maximum angle near thirty 

 degrees, as natural labradorite. If the formula of the oligo- 

 clase be varied in a basic sense, immediately appear microlites 

 of labradorite to the exclusion of anorthite. 



5. Certain mineralogical types absent in, yet suggested by, 

 nature, have frequently been made artificially. Thus have 

 been obtained a pure soda oligoclase, a potash nepheline, 

 showing the relative isomorphism of potash and soda. 



6. On the other hand, certain forms unknown in nature 

 have been obtained artificially, as in the crytallized phosphates 

 of Debray, the sharp-pointed quartz of Hautefeuille, and 

 chalcedonic nepheline of Foque and Levy. 



7. A very considerable service is rendered by mineralogical 

 synthesis by the production of a series more complete than 

 the similar natural one, so the limits of isomorphism are 

 shown with clearness. Thus, Ebelmen completed the spinel 

 series and showed the relation of the ferrites, chromites, and 

 aluminates. The experiments of Hautefeuille, Foque, and 

 Levy, showed the extension of the feldspar family, forming 

 feldspars with bases of lithia, barytes, strontium and lead. 



