Mineral Synthesis. 



05 



four parts of labradorite, and eight parts of leucite. The resulting 

 crystalline product showed in thin sections under the microscope, 

 augite, labradorite, and leucite, in the usual proportion. (See plate IV.) 



Lherzolite. The crystallization of the constituents of this rock, 

 olivine, enstatite, augite, picotite, was easily made. The resulting 

 product differed from the natural rock in a difference in the form of 

 picotite, and in having a greater number of vitreous inclusions. 



Meteorites without feldspar. A mixture of twelve grams of silica, 

 three of magnesia, and five and one-half grams of sesquioxide of iron 

 fused at high temperature and quickly cooled, formed a crystalline 

 mass very like the natural meteorites. 



Meteorites with Feldspar. These types were called eukrites by 

 Rose. They are artificially formed by a fusion, during ninety-six 

 hours, of a mixture of silica, alumina, magnesia, calcium carbonatc 

 and iron sesquioxide. The resulting product in thin sections shows., 

 enstatite, anorthite, olivine, magnetite, and a characteristic ophitic 

 structure. 



Foque and Levy vainly attempted to form by ingeous fusion those 

 rocks which contained quartz, orthoclase, albite, muscovite, biotite, 

 and hornblende. Quartz on fusing lost its power to act on polarized 

 light. The optical properties of orthoclase were changed while albite 

 fused to a glass. Biotite changed to a mass of pleochroic orthorhombic 

 crystals. Microcline fused with muscovite gave an isotropic glass. 

 Four parts of microcline fused with nearly five parts of biotite gave a 

 crystalline mass composed of leucite. olivine, magnetite, melilite, 

 which is a variety of olivine leucitite. 



These negative experiments show that the natural rocks, with 

 quartz, orthoclase, biotite, hornblende, are formed by another method 

 than that of pure igneous fusion. 



Resume. Both the chemical composition and the conditions of 

 cooling influence rock structure. An absence of lime and alkali gi\ r es 

 to lherzolite a granitoid structure. The trachytoid and especially the 

 microlitic structures are very characteristic of the purely igneous rocks. 



To the list of purely igneous rocks there must be added those 

 which show relations to them, though they cannot be reproduced by 

 the same methods. These are the acid rocks, hornblende andesites, 

 trachytes, phonolites, which have not been artificially formed by igneous 

 fusion. These types pass gradually into the more and more acid 



