The chemical testing of minerals in practice is very commonly by the so-called ((blowpipe tests" which possess certain advantages in speed, minute amounts of material needed and in directness of application. Usually no at tempt is made to secure a complete qualitative analysis, but merely to determine the dominat ing constituents. Easy tests exist for most of the common and many of the rare elements, and while group separations, except for in stance into volatile and non-volatile, are not practicable the order of testing is such that certain elements are detected and largely re moved before the tests for the others are made.
4. The Formation and Occurrence of Min The history of a mineral, the rote it has played, is largely told by its occurrence, associates and alterations, and these facts are often illuminated by the successful reproduc tion of a mineral by a method which does not conflict with the known natural conditions. The processes of mineral formation may be broadly grouped under the headings: (1) Crystallization from a fluid magma con sisting chiefly of silicates but partly of oxides, sulphides, fluorides and ferrates mutually dis solved in each other with certain volatile con stituents, chiefly water. By far the greater por tion of the earth's crust has formed from such magmas and a comparatively few mineral groups are found to dominate them. Clarke's estimate* is 1. The feldspars 59.5 per cent.
2. The pyroxenes and amphiboles 16.8 • 3. Ouartz 12.0 • • 4. The micas 3.8 • 5. Accessory minerals 7.9 • • 100.0 • • ===== The estimated 7 per cent of accessory includes rarer silicates, elements, sulphides and oxides, sometimes in quantities which are of economic value, especially when they have undergone a natural concentration known as magmatic segre gation, as in the important nickel ores of Sud bury, Canada.
(2) Formation by pneumatolysis, that is processes in which gases and vapors especially steam, hydrofluoric, boric, suphuric and hydro chloric acid play a principal part. These gases and vapors are released by the cooling magmas and when charged with dissolved matter deposit it later as new minerals in pegmatite veins, con tacts, tin lodes and other places to which they may penetrate. These vapors dissolve, trans port and concentrate minerals rare in the rocks which they penetrate; they form new species into the compositibn of which they enter and they serve as apparently with catalytic action.
(3) Crystallization or precipitation from aqueous solutions. Rain water carrying oxygen and the underground waters with dissolved carbon dioxide and other constituents are the chief agents in the disintegration and altera tion of the minerals which are at or near the surface. They take away selectively much of
the soda, potash and lime and much less of the magnesia and alumina and silica. The solu tions due to this °weathering) are in part re deposited as cements, in part precipitated in the residual minerals, but much is carried away to rivers, lakes or oceans, and there may form deposits of new minerals, such as carbonate of lime in rivers or underground channels. salt or other minerals of soda in lakes (or if boric acid has been present borates may form) and in land-locked basins, great beds of anhydrite. gypsum and common salt, or, more rarely, as at Stassfurt, salts of potassum and magnesium.
The minerals of veins by their composition and arrangement are shown to be deposits from watery solution, but in most cases not simply solutions of the neighboring rocks in the under ground water, but also solutions in the vapors of deep-seated magmas. As the vapors rise into regions of lower pressure and tempera ture condensation takes place, fluid solutions form, various species separate and are de posited on the walls and may ultimately fill the fissure, forming a vein.
Animal and vegetable organisms often assist in the formation of minerals from watery solu tions. The original deposits may not always be strictly mineral species as with coral, shells, diatomaceous earth, but directly or indirectly true species often result, such as limonite, apatite, sulphur and soda nitre. The formation of a mineral may involve very complex agencies such as the combined action of intense pres sure from rock folding and of circulating waters often hot and charged with many constituents, including the so-called mineralizing agents. The new minerals are often denser than the originals and many contain constitutional water.
5. The Uses of The mineral in dustry of this country ranks next to the agri cultural, and the value of the minerals consid erably exceeds $2,000,000,000 a year. While the principal value of these minerals is for the ex traction of particular constituents such as the metals or the substances of use in the chemical industries, there is a large use of the minerals in their natural state not only as constituents of building stones, but as abrasives, fertilizers, fluxes, pigments, refractory materials and in the Ingrig of pottery, porcelain, glass, etc. Minerals susceptible of polish and with any claim to beauty are utilized as precious or orna mental stones.