186 THE EARTH AS MAN'S ABODE ore (bauxite) by the action of water containing cari)on dioxide on feldspar. Tin was early found to alloy with copper to form bronze. Tin does not occur widely. England has some tin mines in Cornwall, but the most important mines lie in a region extending southward from Burma and Siam to the Islands of the Dutch East Indies. There is also a rich deposit 16,000 feet high in the Bolivian Andes. Lead and zinc are two other important metals that man uses today. Deposits of many other metals have been found, and man is constantly seeking new uses for them. Platinum and gold are heavy metals usually found in an uncombined condition in veins where they were deposited or in the bottom of streams where they have settled below the less dense gravel as a result of the erosion of the original lodes. Both gold and silver are deposited in fissures from solutions working upwards from lower deposits. The original "mother lode" in California, about a mile wide and a hundred miles long, contains gold-bearing veins whose content per ton is worth about $3.00 or $4.00 or more; but the disintegration of large portions of this mother lode, followed by the sorting-out processes of erosion, produced fabulous gold deposits, some of which were worth $200 to $300 per shovelful. Today man is working the richer mother-lode veins, duplicating the processes of nature. The ore is crushed to a fine powder in stamp mills; and then it is either mixed with water and run over concentrating tables, where the heavier gold and silver minerals separate out by gravity, or it is mixed with chemicals which cause these minerals to float ofif in a froth. Frequently the powder from the stamp mills is mixed with water and run over a sloping copper plate coated with mercury, which retains the gold as it settles out of the mixture. Man sometimes even resorts to the chemical-decomposition processes and dissolves the gold with cyanide. The gold is then precipitated from the cyanide solution by adding finely divided zinc. Colin G. Fink has predicted that the next age will be that of aluminum. It is the most abundant metal in the earth's crust. There are 8 pounds of aluminum for every 5 pounds of iron and every 0.002 pound of copper. The known supplies of copper at the 1929 rate of consumption will last only 40 or 50 years. The history of man is closely tied up with that of the prospector in his search for new deposits of metals. Vast Deposits of Useful Salts Have Been Found. Some of the salt deposits were formed under conditions which caused the different salts in the ocean water to separate out one at-a time.
MANY VALUABLE MINERALS 187 At some places Epsom salts and gypsum (magnesium and calcium sulfates) have been formed. At other locations borax and soda have been deposited. Some of the richest deposits of borax and soda in the world have been located in the ancient lakes of the Mojave Desert, which acted as great catch basins for the water from the surrounding mountains. Twenty billion tons of valuable potassium salts were formed by the evaporation of a great inland sea to form the present great Stassfurt deposits in Germany. Similar deposits have been found far underground extending for many miles under portions of Oklahoma and Texas. Another exceedingly valuable product, common salt, is obtained in some sections of the world today by the evaporation of ocean water or desert lakes or the water pumped from wells. Salt has been laid down in huge deposits in many parts of the world by the evaporation of inland seas. It has been estimated that if the salt in the ocean were separated by evaporation, there would be an amount sufficient to cover the surface of the earth to a depth of 112 feet. Sulfur Is an Important Mineral. Volcanic activities have produced large deposits of sulfur which were formed by the cooling or the interaction of volcanic gases. The action of carbon compounds with gypsum is thought to be responsible for the huge underground deposits of sulfur in Precious Stones Are Valuable Because of Their Beauty. Louisiana and Texas. During all recorded history man has valued jewels and precious stones. He has valued them for their beauty and has often endowed them with imagined powers for good or evil. Only three minerals possess the requirements, beauty, durability, and rarity, which characterize precious gems; the precious gems are diamond, corundum, and beryl. The ruby and sapphire are varieties of corundum, while the emerald is a variety of beryl. Beauty is associated with such factors as color, luster, transparency, and sparkle. The beauty of the diamond is due to the last three of the above factors, while the beauty of the emerald is due chiefly to its green color. All gem stones are sold on the basis of the carat/ which is 200 milligrams in weight. A gem is any mineral, precious or otherwise, which has been polished. When a gem has been cut and mounted in some kind of setting, it is called a jewel. 1 Do not confuse this term with the carat of gold fineness.