Mineralizers

Combining mineralizers and 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 exceptionally 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 elemehts 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-forming minerals in very small quantities, as the micas always contain small amounts of hydroxyl and fluorine, apatite contains fluorine and chlorine, and tourmaline contains boron as a molecular essential.

Mineralizers are fluxes in that they decrease the viscosity 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 temperature 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 complex nature, and it is not possible for them to form at the temperature of their freezing point. Such minerals are termed the low temperature minerals. Their molecules are considered to be more complex than those which form from direct fusion and without the aid of mineralizers, or the high temperature minerals. In the low temperature minerals are included the amphiboles, micas, sodalites, nephelinc, tourmaline, topaz, beryl, titanite, quartz, albite, and orthoclase, and also many rare minerals of the pegmatites. In the synthesis of this class a mineralizer must usually be present, cither to lower the fusing point or to reduce the viscosity of the melt, while some, as topaz, tourmaline, and muscovite, have never been produced artificially.

That mineralizers have been present during the stage of crystallization of such rocks as granite, syenite, and pegmatites is shown by the simple fact that the quartz of such rocks always contains numerous cavities holding liquid inclusions, and that the micas contain hydroxyl and fluorine. The mineralizer is usually a volatile substance or forms volatile compounds with the bases as the fluorides, and therefore when the magma is extruded they escape, and with their escape the tendency to quickly solidify and the formation of glass is increased. Basalts are more often crystallized than are the rhyolites and andesites, as in the latter the mineralizers have escaped, leaving the magma by nature too viscous to crystallize. The coarse crystalline forms, granite and syenite, are plutonic rocks and have crystallized under conditions which preclude any escape of the volatile mineralizers, or they have escaped very slowly.

In the process of cooling, those compounds which are the more insoluble have separated first, with the result that the remaining liquid portion is a concentrated solution of the more soluble, and the dykes, veins, and marginal masses connected with some granites and known as pegmatites are the result of and represent the ultimate concentration of some of the constituents of the original fused magma. Crystals of pegmatites are large and well formed, and such dykes contain minerals in quantity which are rare accessories in the rock mass as a whole. There seems to be no good reason why the condition should not change during crystallization from that at the beginning, a fused magma, at a high temperature, far above the critical temperature of water, 305° C., to that at the end, when the final product of crystallization maybe separated from a solution in water, though hot and under pressure.