5* 



Cincinnati Society of Natural History. 



MINERAL SYNTHESIS. 

 By G. Perry Grimsley, Ph. D. 

 (Continued from Vol. XVI, p. 169.) 

 III. 



EXPERIMENTS AND RESULTS. 



The history and methods of mineral synthesis have been out- 

 lined in a former paper. It is proposed in the present article to give 

 an account of a number of important experiments and the results of 

 the work. 



The crystals formed by artificial synthesis are neither large in 

 size nor of great beauty. The process of sublimation furnishes the 

 largest specimens but nearly all these crystals must be studied under 

 the microscope. The size, beauty and perfection of the crystals 

 depend on the methods and apparatus used in their formation. In 

 many cases these properties seem to be intimately connected with the 

 nature of the bodies. Thus it is more difficult to obtain good 

 crystals of leucite than of nepheline. Magnesian mica (biotite) 

 crystallizes more easily than the lithium mica (zinnwaldite). It is more 

 difficult to obtain the alumina and sodium pyroxenes in crystalline 

 aggregates than the magnesia and iron varieties. Among feldspars 

 anorthite is most easily formed; among the zeolites, analcite ; among 

 potassium and magnesian silicates, olivine; among sodium and 

 aluminum silicates, nepheline. 



Very interesting and instructive for study are the growth forms 

 shown when the reaction is slow in crystallizing from fusion or chem- 

 ical precipitation. These rudimentary forms may be observed, 

 perhaps best, in the minerals leucite and nepheline. 



A careful comparison of the methods and results of synthesis 

 shows a marked influence of the manner of formation on the crystal 

 habit or form in very many crystals. Sodium chloride (common salt) 

 generally occurs in cubes, yet from a caustic soda or ammonia solution 

 octahedra are formed. When augite is crystallized rapidly from fusion 

 long lath crystals are formed with characteristic augitic combination 

 of planes; but if the augite is formed by slow crystallization, the 

 forms are short thick prisms or grains. One of the best illustrations 



