246 MINERALOGY 



those containing felspathoids, silica or alkali feldspars, when under 

 the same conditions. 



In the synthesis of minerals it has been proven without doubt 

 that certain minerals are easily formed from a simple fusion, com- 

 posed of their chemical constituents in correct proportions ; in 

 all cases these fusions are not highly viscous in nature. The 

 plagioclases, magnetite, hematite, rutile, spinels, corundum, some 

 garnets, leucite, olivine, and enstatite have all been formed from 

 simple fusions in an open crucible. They are all rock-forming 

 minerals, and in nature they have in many occurrences been crys- 

 tallized directly from a fused magma. 



Mineralizers. On the other hand there is a group of minerals 

 which it has been impossible to synthesize by the open fusion 

 method, as there is contained in their molecule small amounts of 

 volatile compounds as fluorine, water as hydroxyl, or chlorine; 

 or again the fusion at the point or temperature of crystallization 

 is so viscous as to prevent the formation of crystals, when the fusion 

 cools as a glass. Many granites, syenites, and gabbros are excep- 

 tionally well crystallized, and contain orthoclase, albite, quartz, 

 amphibole, and micas, minerals which from the experience with 

 open crucible fusions of their chemical components cannot be 

 crystallized, and the formation of crystals requires other substances 

 to be present in the fusion, as water, fluorine, boron, chlorine, 

 tungsten, etc., even though these elements are not a part of the 

 mineral molecule formed. Such elements are termed mineralizers 

 from the role they play in the formation of certain minerals. 

 They do, however, enter the molecule of some of these rock-form- 

 ing minerals in very small quantities, as the micas always con- 

 tain small amounts of hydroxyl and fluorine, apatite contains 

 fluorine and chlorine, and tourmaline contains boron as a molecu- 

 lar essential. 



Mineralizers are fluxes in that they decrease the viscosi.ty of 

 magmas in the same sense that fluorite is used in many smelting 

 operations to attain the same end, that of forming a liquid slag. 

 They are solvents in the same sense that water is a solvent for salt 

 in the two-component system illustrated, and in each case they lower 

 the fusing point or the temperature of separation to such an extent 

 that it is possible for molecules to form at a much lower tempera- 

 ture and at temperatures far below their actual melting points, 

 as many minerals are unstable at their temperature of fusion and 

 break down into components formed of molecules of a less com- 



