DISTRIBUTION OF THE ELEMENTS. a

The elements differ widely in their abundance and in their mode of distribution in nature. Under the latter heading the more important data may be summarized as follows:

Aluminum.-The most abundant of all the metals. An essential constituent of all important rocks except the sandstones and limestones, and even in these its compounds are common impurities. Being easily oxidized, it nowhere occurs native. Found chiefly in silicates, such as the feldspars, micas, clays, etc.; but also as the oxide, corundum; the hydroxide, bauxite; as fluoride in cryolite; and in various phosphates and sulphates. With the exception of the fluorides, only oxidized compounds of aluminum are known to exist in

nature.

Antimony.-Common, but neither abundant nor widely diffused. Found native, more frequently as the sulphide, stibnite, also in various antimonides and sulphantimonides of the heavy metals, and as oxide of secondary origin. The minerals of antimony are generally

For an early table showing distribution, see Élie de Beaumont, Bull. Soc. géol., 2d ser., vol. 4, p. 1333, 1846-47.

found in metalliferous veins, but the amorphous sulphide has been observed as a deposit upon sinter at Steamboat Springs, Nevada.

Argon. An inert gas that forms nearly 1 per cent of the atmosphere, and is also sometimes found in mineral springs. No compounds of argon are known.

Arsenic. Found native, in two sulphides, in various arsenides and sulpharsenides of the heavy metals, as oxide, and in considerable number of arsenates. Arsenopyrite is the commonest arsenical mineral. Arsenic is very widely diffused and traces of it exist normally even in organic matter. It is not an uncommon ingredient in mineral, especially thermal, springs. In its chemical relations it is regarded as nonmetallic and closely allied to phosphorus.

Barium.-Widely distributed in small quantities throughout the igneous rocks, probably as a minor constituent of the feldspars and micas, although other silicates containing barium are known. Commonly found concentrated as the sulphate, barite, or as the carbonate, witherite. This element occurs only in oxidized compounds.

Bismuth.-Resembles antimony in its modes of occurrence, but is less common. Native bismuth and the sulphide, bismuthinite, are its chief ores. Two silicates of bismuth, several sulphobismuthides, and the telluride, oxide, carbonate, vanadate, and arsenate exist as relatively rare mineral species.

Boron. An essential constituent of several silicates, notably of tourmaline and datolite. Its compounds are obtained commercially from borates, such as borax, ulexite, and colemanite, or from native orthoboric acid, sassolite, which is found in the waters of certain volcanic springs. Some alkaline lakes or lagoons, especially in California and Tibet, yield borax in large quantities.

Bromine.-Found in natural waters in the form of bromides. Sea water contains it in appreciable quantities, and much bromine has been extracted from the brine wells of West Virginia and Michigan. The bromide and chlorobromide of silver are well-known ores.

Cadmium.-A relatively rare metal found in association with zinc, which it resembles. Occurs generally as the sulphide, greenockite. Casium. A rare metal of the alkaline group, allied to potassium. Often found in lepidolite, and in the waters of some mineral springs. The very rare mineral pollucite is a silicate of aluminum and cæsium.

Calcium. One of the most abundant metals, but never found in nature uncombined. An essential constituent of many rock-forming minerals, especially of anorthite, garnet, epidote, the amphiboles, the pyroxenes, and scapolite. Limestone is the carbonate, fluor spar is the fluoride, and gypsum is the sulphate of calcium. Apatite is the fluophosphate or chlorophosphate of this metal. Many other mineral species also contain calcium, and it is found in nearly all

natural waters and in connection with organized life, as in bones and shells. Calcium sulphide has once been identified in a meteorite. Carbon. The characteristic element of organic matter. In the mineral kingdom carbon is found crystallized as graphite and diamond and also amorphous in coal. Carbon dioxide is a normal constituent of atmospheric air. Natural gas, petroleum, and bitumen are essentially hydrocarbons. Carbonic acid and carbonates exist in most natural waters, and great rock masses are composed of carbonates of calcium, magnesium, and iron. A few silicates contain carbon, but of these, cancrinite is the only species having petrographic importance.

Cerium.-One of the group of elements known as the metals of the rare earths. These substances are generally found in granites or elæolite syenites, or in gravels derived therefrom. Cerium exists in a considerable number of mineral species, but the phosphate, monazite, and the silicates, cerite and allanite, are all that need be mentioned here.

Chlorine. The most abundant element of the halogen group. Commonly found as sodium chloride, as in sea water and rock salt. Also in certain rock-forming minerals, such as sodalite and the scapolites, and in a variety of other minerals of greater or less importance. Silver chloride, for example, is a well-known ore, and carnallite is valuable for the potassium which it contains.

Chromium. Very widely diffused, generally in the form of chromite, and most commonly in magnesian rocks. A few chromates and several silicates containing chromium are also known, but as relatively rare minerals.

Cobalt.-Less abundant than nickel, with which it is generally associated. Usually found as sulphide or arsenide, or in oxidized salts derived from those compounds.

Columbium.-A rare acid-forming element resembling and associated with tantalum. Both form salts with iron, manganese, calcium, uranium, and the rare-earth metals, the minerals columbite, tantalite, and samarskite being typical examples. All these minerals are most abundant in pegmatite veins.

Copper.-Minute traces of this metal are often detected in igneous rocks, although they are rarely determined quantitatively. Also present in sea water in very small amounts. Its chief ores are native copper, several sulphides, two oxides, and two carbonates. The arsenides, arsenates, antimonides, phosphates, sulphates, and silicates also exist in nature, but are less important. In chalcopyrite and bornite, copper is associated with iron.

Dysprosium.-A little-known metal of the rare earths.

Erbium.-One of the rare-earth metals of the yttrium group. See "Yttrium."

Europium. Another metal of the rare earths, of slight importance. Fluorine. The most characteristic minerals of fluorine are calcium fluoride (fluor spar) and cryolite, a fluoride of aluminum and sodium. Apatite is a phosphate containing fluorine, and the element is also found in a goodly number of silicates, such as topaz, tourmaline, the micas, etc. Fluorine, therefore, is commonly present in igneous rocks, although in small quantities.

Gadolinium.-One of the metals of the rare earths. See "Cerium" and "Yttrium."

Gallium.-A very rare metal whose salts resemble those of aluminum. Found in traces in many zinc blendes. Always present in spectroscopic traces in bauxite and in nearly all aluminous

minerals.

Germanium.-A very rare metal allied to tin. The mineral argyrodite is a sulphide of germanium and silver.

Glucinum.-A relatively rare metal, first discovered in beryl, from which the alternative name beryllium is derived. Found also in the aluminate, chrysoberyl; in several rare silicates and phosphates; and in a borate, hambergite. As a rule the minerals of glucinum occur in granitic rocks.

Gold. Found in nature as the free metal and in tellurides. Very widely distributed and under a great variety of conditions, but almost invariably associated with quartz or pyrite. Gold has been observed in process of deposition, probably from solution in alkaline sulphides, at Steamboat Springs, Nevada. It is also present, in very small traces, in sea water.

Helium. An inert gas obtained from uraninite. The largest quantities are derived from the highly crystalline uraninite found in pegmatite. The massive mineral from metalliferous veins contains little or no helium. Traces of helium also exist in the atmosphere, in spring waters, and in some samples of natural gas. Holmium.-One of the rare-earth metals. Little known. Hydrogen. This element forms about one-ninth part by weight of water, and therefore it occurs almost everywhere in nature. In a majority of all mineral species, and therefore in practically all rocks, it is found, either as occluded moisture, as water of crystallization, or combined as hydroxyl. All organic matter contains hydrogen, and hence it is an essential constituent of such derived substances as natural gas, petroleum, asphaltum, and coal. The free gas has been detected in the atmosphere, but in very minute quantities.

Indium.-A rare metal, found in very small quantities in certain zine blendes. Spectroscopic traces of it can be detected in many minerals, especially in iron ores.

Iodine. The least abundant element of the halogen group. Found in sea water, in certain mineral springs, and in a few rare minerals, especially the iodides of silver, copper, and lead. Calcium iodate, lautarite, exists in the Chilean nitrate beds.

Iridium. A metal of the platinum group. See "Platinum." Iron. Next to aluminum, the most abundant metal, although native iron is rare. Found in greater or less amount in practically all rocks, especially in those which contain amphiboles, pyroxenes, micas, or olivine. Magnetite and hematite are oxides of iron, limonite is a hydroxide, pyrite and marcasite are sulphides, siderite is the carbonate, and there are also many silicates, phosphates, arsenates, etc., which contain this element. The mineral species of which iron is a normal constituent are numbered by hundreds.

Krypton.-An inert gas of the argon group, found in small quantities in the atmosphere.

Lanthanum.-A metal of the rare-earth group, almost invariably associated with cerium, q. v.

Lead.-Found chiefly in the sulphide, galena, from which, by alteration, various oxides, the sulphate, and the carbonate are derived. Native lead is rare. A number of sulphosalts are known, several silicates, and also a phosphate, an arsenate, and a vanadate. Galena is frequently associated with pyrite, marcasite, and sphalerite.

Lithium.-One of the alkaline metals. Traces of it are found in nearly all igneous rocks, and in the waters of many mineral springs. The more important lithia minerals are lepidolite, spodumene, petalite, amblygonite, triphylite, and the lithia tourmalines.

Magnesium. One of the most abundant metals. In igneous rocks it is represented by amphiboles, pyroxenes, micas, and olivine. Talc, chlorite, and serpentine are common magnesium silicates, and dolomite, the carbonate of magnesia and lime, is also found in enormous quantities. Magnesium compounds occur in sea water and in many mineral springs. The metal is not found native.

Manganese.-Widely diffused in small quantities. Found in most rocks and in some mineral waters. Never native. Occurs commonly in silicates, oxides, and carbonates, less frequently in sulphides, phosphates, tungstates, columbates, etc. The dioxide, pyrolusite, and the hydroxide, psilomelane, are the commonest manganese minerals. Mercury. This metal is neither abundant nor widely diffused. Exists as native mercury, but is usually found, locally concentrated, in the form of the sulphide, cinnabar. Chlorides of mercury, the selenide and the telluride, are relatively rare minerals. Cinnabar has been observed in process of deposition by solfataric action at Sulphur Bank, California; and Steamboat Springs, Nevada.