Zirconium

“ Artificial crystals of zircon have been obtained by the action of silicon tetrachloride and silicon tetrafluoride on zirconia, and by the action of zirconium tetrafluoride on silica at high temperatures.
Zircon is one of the most widely distributed minerals known, though usually it occurs in very small quantities. Good crystals have been found in New Zealand, in Ceylon, at Miask in the Urals, and in North Carolina. This last deposit has been worked commercially for the extraction of zirconia for Nernst lamps (vide p. 320) . ”

“ Thorium and titanium accompany the zirconium, but iron, aluminium, and the rare earths remain in solution. Another method depends on the fact that zirconium is not precipitated from alkaline solution by ammonium sulphide in the presence of tartaric acid, whereas this reagent does not inhibit the precipitation of ferrous sulphide. Iron may also be removed from a solution in concentrated hydrochloric acid by means of ether, in which medium ferric chloride is easily soluble. Zirconium compounds may be obtained free from iron by repeated crystallisations of the oxychloride. ”

“ The powdery metal burns readily in air, the crystalline metal requires to be heated in an oxyhydrogen flame before it catches fire. Mineral acids generally attack the crystallized metal very little even in the heat; aqua regia, however, dissolves it readily, and so does hydrofluoric acid. In its chemical affinities zirconium resembles titanium, cerium and thorium; it occurs in company with these elements, and is tetravalent in its more important salts.
Zirconium oxide or zirconia, ZrO2, has become important since its application to the manufacture of mantles for incandescent gas-lighting. ”

“ Zir"co- (?) . (Chem.) A combining form (also used adjectively) designating zirconium as an element of certain double compounds; zircono-; as in zircofluoric acid, sodium zircofluoride.
Zir`co*flu"or*ide (?) , n. (Chem.) A double fluoride of zirconium and hydrogen, or some other positive element or radical; as, zircofluoride of sodium.
Zir"con (?) , n. [F., the same word as jargon. See Jargon a variety of zircon.] (Min.) A mineral occurring in tetragonal crystals, usually of a brown or gray color. It consists of silica and zirconia. A red variety, used as a gem, is called hyacinth. ”

“ When heated in a current of hydrogen at a red heat, it forms the hydride, ZrH2, [462] as a velvet-black powder, which burns with an intense bluish flame in oxygen, forming the sesquioxide, Zr2O3. When heated in nitrogen or ammonia, amorphous zirconium yields nitrides, which are also obtained when any attempt is made to reduce zirconium compounds to the metal in air. The most definite is the compound Zr2N3, [462] which forms a bronze-coloured powder, resistant to all mineral acids except hydrofluoric acid. Chlorine and bromine transform this to the halide. ”

“ Zirconium is always, with the doubtful exception of its peroxy-compounds and the lower oxides, tetravalent. Cerium, as already described, can form two series of compounds, in which it is respectively tri- and tetravalent; thorium, like zirconium, is always tetravalent.
Titanium, Ti = 48·1
Though generally classed among the rare elements, titanium is probably at least as widely distributed in nature as most of the common metals. It occurs as the dioxide in small quantities in all the common silicate rocks and minerals, and in traces in the animal and vegetable kingdoms ”

“ These are of great importance, and include manganese, chromium, nickel, tungsten, vanadium, antimony, molybdenum, uranium, and zirconium. Radium is closely associated with uranium and is considered with it. Closely allied with zirconium are thorium and mesothorium, and their treatment therefore closely follows that of zirconium.
The next great group is that of the major metals, other than iron and the ferro-alloy metals: copper, lead, zinc, tin and mercury, and aluminum. Aluminum ores are used not only as sources of the metal, but for the manufacture of refractories and abrasives. ”

“ The solubility of zirconium and thorium salts in excess of alkali oxalate or carbonate is also in harmony with the less pronounced electropositive character of these elements. The sulphates of titanium and zirconium appear to be of complex constitution, whilst their neutral chlorides cannot be obtained from solution. As is to be expected from its high atomic weight, thorium approaches most nearly to the rare earths in chemical properties ”

“ It occurs in some silicates, and in small quantities in almost all the rare earth minerals. The most important source of the element and its compounds was until quite recently the mineral Zircon, with its gem-varieties Hyacinth and Jargon, and the large number of secondary altered zircon minerals. Since its discovery in 1892, however, the naturally occurring oxide, Baddeleyite, [455] has become increasingly important for the extraction of zirconium compounds, especially for the preparation of the pure oxide for fire-resistant materials. ”

“ The hydroxide readily loses its water at a dull red heat and passes into an hydride with vivid incandescence. Zirconia can be obtained crystalline, in a form isomorphous with cassiterite and rutile, by fusing the amorphous modification with borax, and dissolving out with sulphuric acid. The anhydrous oxide is with difficulty soluble even in hydrofluoric acid ”

“ It is notable that the specific gravity has a very wide range, extending from a little below 4 to rather more than 4·7, and being thus greater than that of any other gem-stone. Rarely colourless, zircon is usually brown or red, sometimes orange, yellow or green, and occasionally parti-coloured or zoned.
Whilst common zircon is opaque, the gem-varieties are transparent. The dichroism of coloured zircons is always feeble; the double refraction usually strong and of positive sign; and the optical properties of some zircons suggest a biaxial mineral. ”

“ The effect of heat on zircon is remarkable. Most coloured zircons, exposed to a high temperature, either change or lose their colour, but this loss is attended by a gain in brilliancy. The “Matura diamonds” of Ceylon are zircons which have been thus artificially decolorized. Certain zircons when heated in a Bunsen-flame glow with an orange incandescence, whilst others may emit an orange glow when ground on a copper-wheel fed with diamond-dust. Even exposure to sunlight will sometimes modify the colour and lustre of a zircon. ”

“ The minerals may be treated by any of the usual methods. Zircon may be fused with alkali or alkali carbonate; the cooled melt is extracted with water, and the insoluble alkali zirconate decomposed by dilute acids; from the solution, zirconia is thrown down by alkalies. Potassium hydrogen fluoride and potassium hydrogen sulphate may be used for the treatment either of zircon or of baddeleyite; in the first case, the potassium fluozirconate formed may be dissolved by boiling with dilute hydrofluoric acid, and separates out readily on cooling, whilst the fluosilicate formed is not dissolved ”

“ Some [252] dark quartz yields a nearly garnet red product, after heating.
Zircon. Slight increase in temperature causes many of the zircons from Ceylon to change markedly in color. An alcohol flame serves admirably to effect the change, care being taken to warm up the stone very gradually and to cool it slowly. Drafts should be prevented, as they might suddenly cool the stone and crack it. Some zircons become completely whitened by this treatment. At the same time they increase markedly in density and in refractive index and thus become even more snappy and brilliant than when colored. ”

“ Brown zircon, while lacking dichroism, is frequently rich and pleasing in shade, and when well cut is very snappy, the luster being almost adamantine, the dispersion being large, and the refractive index high. It is useless to deny that by the unaided eye one might be deceived into thinking that a fine brown zircon was a brown diamond. However, the large double refraction of the zircon easily distinguishes it from diamond (use the sunlight-card method or look for the doubling of the edges of the rear facets as seen through the table) . ”

“ Having observed, for example, that the syenitic granite of Norway, in which the mineral called zircon abounds, has altered the Silurian strata wherever it is in contact, we do not hesitate to refer other masses of the same zircon-syenite in the south of Norway to a post-Silurian date. Some have imagined that the age of different granites might, to a great extent, be determined by their mineral characters alone; syenite, for instance, or granite with hornblende, being more modern than common or micaceous granite. ”

“ Geological criticism tends to lessen the trustworthiness of the conclusions; it is pointed out that the age of a specimen of zircon is not necessarily that of the rock in which it occurs, for zircon is an extremely stable mineral, and might survive unchanged several fusions and re-crystallisations of the magma. Strutt replies to this that at the temperature of fusion of a rock, zircon would certainly give up its accumulated helium, so that the age determined from the helium content would be that of the last fusion, i.e. ”

“ The accessory minerals include sphene (very frequent) , apatite, zircon, magnetite and pyrites; quartz as above stated is rarely absent but should never be abundant, otherwise the rock becomes a granite. Nepheline and sodalite occur only in those rocks which show transitions to the nepheline-syenites.
The structure of syenites is almost exactly the same as that of the granites; varieties with porphyritic felspar are known but none of these rocks are evenly granular. The apatite, zircon and magnetite crystallize first, and occur as small well-shaped crystals enclosed in the other minerals. ”

“ Zircon is an invariable constituent of these ‘monazite sands,’ as such deposits are called; and others almost as frequently found are rutile, ilmenite, sphene (titanite) , and apatite. Common, too, are the characteristic minerals of the metamorphic rocks, garnet, epidote, sillimanite, tourmaline, etc. Rare earth minerals found in the monazite sands include xenotime, fergusonite, [91] samarskite, gadolinite, and allanite. The remaining minerals are oxides of iron and tin, with, of course, a considerable amount of quartz. ”

“ Such stones originally were reddish brown zircon pebbles from Indochina, but they have been converted by being subjected to temperatures 57 approaching 1800° F. for periods of up to two hours. When the original zircons are heated in a closed container, the stones become blue or colorless; when a flow of air is allowed through the container, the stones become golden yellow, red, or colorless. In most of these converted stones the color remains quite stable, but in some it may revert to an unattractive greenish or brownish blue after a period of time. ”

“ A few zircons, a fraction of a millimeter in size but perfect in form, were found associated with others rounded on their solid angles and edges. The crystals are of the common short form and bear the usual faces in a greater or less degree of development. Pyramids of the first and second order alternate in magnitude; pinacoid encroaches upon prism, and vice versa.
Quartz constitutes by far the largest proportion of the minerals, both in bulk and in weight. It is always fragmental; sometimes water-clear, but chiefly occurs in opaque grains of different colors. ”

“ The whitened zircon, when finely cut in the brilliant form, with truly flat facets and sharp edges and with a top angle of about 39 degrees and a back angle of about 44 degrees, so closely resembles a diamond that it will deceive almost anyone on casual inspection. The expert, even, may be deceived, if caught off his guard. The writer has a fine specimen of a little over one carat, with which he has deceived many jewelers and pawnbrokers, and even an importer or two. ”

“ We know that quartz requires a higher temperature to melt it than does either the feldspar or the mica, and so, had the granite been formed as are regular volcanic rocks in the ordinary way of igneous fusion, we should certainly have found that the quartz would have crystallized before either the feldspar or the mica, and it would have been seen in definite crystalline form, and its crystals would have interfered with and penetrated those of the other mineral constituents of the rock. ”

“ There are also other decided examples among the transparent minerals to sustain this view; the most remarkable of which perhaps may be found in the zircon, a [Pg 94] gem which is soft as quartz; yet it ranks next to the diamond in brightness, and far surpasses in eclat every other gem, even the sapphire, which is next to the diamond in hardness. Density does not seem to have anything to do with the determination of the refractive power of gems, for the garnet, spinel, sapphire, and zircon are much heavier than the diamond, and are yet far inferior in brilliancy. ”

“ But neither the transparency of the quartz nor the silvery lustre of the mica can be expressed in the engraving.
The uniform mineral character of large masses of granite seems to indicate that large quantities of the component elements were thoroughly mixed up together, and then crystallised under precisely similar conditions. There are, however, many accidental, or “occasional,” minerals, as they are termed, which belong to granite. Among these black schorl or tourmaline, actinolite, zircon, garnet, and fluor spar are not uncommon ”

“ Quartz, dense and milky, also in quartz of nearly every colour and appearance, saccharoidal, crystalline, nay, even in clear glass-like six-sided prismatic crystals, and associated with silver, copper, lead, arsenic, iron as sulphide, oxide, carbonate, and tungstate, antimony, bismuth, nickel, zinc, lead, and other metals in one form or another; in slate, quartzite, mica schist, granite, diorite, porphyry, felsite, calcite, dolomite, common carbonate of iron, siliceous sinter from a hot spring, as at Mount Morgan; as alluvial gold in drifts formed of almost all these materials ”