It has further been possible to show within the last two years that rock formation in which volatile ingredients play a necessary and determining part can be completely studied in the laboratory with as much precision as though all the components were solids or liquids.
Along with the laboratory work on the formation of minerals and rocks has gone an increasing amount of field work on the activities of accessible volcanoes, such as Kilauea and Vesuvius, where the fusion and recrystallization of rocks on a large scale can be observed and studied.
There was once a time when the confidence of the laboratory in the capacity of physics and chemistry to solve geological problems was not shared by all geologists. There were some who were inclined to view with considerable apprehension the vast ramifications and complications of natural rock formation as a problem impossible of adequate solution in the laboratory. It is, therefore, a matter of satisfaction to all those who have participated in these efforts to see the evidences of this apprehension disappearing gradually as the work has progressed. A careful appraisement of the situation to-day, after ten years of activity, reveals the fact that the tangible grounds for anxiety about the accessibility of the problems which were confronted at first are now for the most part dissipated.
It will not be possible to review in detail the lines of work sketched above. An outline of the synthetic work on systems of the mineral oxides and a paragraph on the volcano researches will perhaps suffice to indicate the general plan and purpose of the laboratory’s work. It should be added that the results of many of the researches of the laboratory, detailed below, have been published in the pages of the Journal (see 21, 89, 1906, and later volumes).
Mineral Researches.—The mineral studies include:
I. One-component systems: silica, with its numerous polymorphic forms and their relations to temperature and the conditions of rock formation; alumina; magnesia; and lime.
II. Two-component systems: silica-alumina, including sillimanite and related minerals; silica-magnesia, including the tetramorphic metasilicate MgSiO3; silica-lime, including wollastonite; the alkali silicates, particularly with reference to their equilibria with carbon dioxide and with water; ferric oxide-lime; alumina-lime; alumina-magnesia, including spinel; and hematite-magnetite, a solid-solution series of an unusual type.
III. Three-component systems: silica-alumina-magnesia, completed but not yet published; silica-alumina-lime, complete, including the compounds that enter into the composition of portland cement; silica-magnesia-lime, completed but not yet published, including, however, published work on the diopside-forsterite-silica system, and on the CaSiO3-MgSiO3 series; and alumina-magnesia-lime.
IV. Four components: SiO2-Al2O3-MgO-CaO: the incomplete system anorthite-forsterite-silica; SiO2-Al2O3-CaO-Na2O: the series of lime-soda feldspars (albite-anorthite), and the series nephelite (carnegieite)-anorthite; SiO2-Al2O3-Na2O-K2O: the sodium-potassium nephelites.
V. Five components: SiO2-Al2O3-MgO-CaO-Na2O: the ternary system diopside-anorthite-albite (haplo-basaltic and haplo-dioritic magmas).