Zirconium - Element information, properties and uses | Periodic Table Chemistry in its element: zirconium (Promo) You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry. (End promo) Chris Smith Hello and welcome to our tour of the unusual, exciting and deadly aspects of the elements that make up the world around us. We're kicking off our journey through the Periodic Table with a chemical that sometimes masquerades as diamond but is equally at home in the core of a nuclear reactor or even in an ironworks. To tell the story of this mysterious entity which is otherwise known as zirconium, here's chemist and award winning author John Emsley. John Emsley Zirconium. Wear it flashing on your finger, or unseen within your frame, it holds the key to nuclear energy, and it's got a gem-like name. It's zirconium. The name zirconium comes from the Arabic word zargun which refers to a golden-hued gemstone known since Biblical times called zircon.

Today artificial gems are made from Zirconium oxide known as cubic zirconia and they sparkle with more brilliance than diamond although they are not as hard. What distinguishes them from real diamond is their higher density of 6.0 g cm-3 compared to diamond's 3.52. Zirconium is abundant in S-type stars in which heavier elements are formed by neutron capture. Traces are also present in the Sun. Rock brought back from the moon was found to have a surprisingly high zirconium content. Down here on Earth zircons has shown that life might have started much earlier than once thought. These were found in Australia in the year 2000 were 4.4 billion years old, and their oxygen isotope ratio of O16/O18 showed they could only have been formed when there was liquid water on the surface of the Earth, and this was nearly 500 million years earlier than previously assumed.

In the Middle Ages colourless gemstones of zircon were thought to be an inferior kind of diamond, but that was shown to be wrong when a German chemist, Martin Klaproth (1743-1817), analysed one in 1789 and discovered zirconium. Klaproth was unable to isolate the metal itself. That was achieved in 1824 by the Swedish chemist Jöns Jacob Berzelius but there was little use for it or its chemical compounds, and so it languished for a century or more. Today this element is widely used, as zircon, as Zirconium oxide and as the metal itself. Zirconium is to be found in ceramics, foundry equipment, glass, chemicals, and metal alloys. Zircon sand is used for heat-resistant linings for furnaces, for giant ladles for molten metal, and to make foundry moulds. Mixed with vanadium or praseodymium zircon makes blue and yellow pigments for glazing pottery and tiles. Zirconium oxide is used to make heat resistant crucibles, ceramics and abrasives. A red-hot crucible made from it can be plunged into cold water without cracking.

Zirconium oxide is to be found in ultra-strong ceramics that are stronger and sharper even than toughened steel and are used for knives, scissors and golf irons. Production of pure zirconium oxide is almost 25 000 tons per year, and it also goes into various chemicals that end up as cosmetics, antiperspirants, food packaging, and even fake gems. The paper and packaging industry is finding zirconium compounds make good surface coatings because they have excellent water resistance and strength. Equally important is their low toxicity. Zirconium metal has an oxidised surface which is both hard and impervious to chemical attack making it ideal not only for chemical plants but for body implants such as hip replacement joints. Zirconium-aluminium alloy is used for top of the range bicycle frames because it combines strength and lightness. Zirconium metal had some hidden assets which suddenly brought it to prominence in the late 1940s; it was found to be the ideal metal for inside nuclear reactors and nuclear submarines. It does not corrode at high temperatures, nor absorb neutrons to form radioactive isotopes.

Even today the nuclear industry buys almost all of the metal that is produced and some nuclear reactors have more than 100 kilometres of zirconium tubing. Zirconium is used to make the cladding for uranium oxide fuel elements. As mined, zirconium contains 1-3% per cent of hafnium, which is chemically very similar, and although it is difficult to separate the two elements this has to be done for the metal used in the nuclear industry because hafnium absorbs neutrons very strongly. Finally, we have two zirconium materials with extreme properties, one which it displays when very cold, the other when it is heated to high temperatures. The first is a zirconium-niobium alloy which becomes superconducting below 35 Kelvin (- 238oC) in other words it will conduct electricity with no loss of energy. The second is zirconium tungstate (ZrW2O8) which actually shrinks as you heat it up, at least until it reaches 700oC when it decomposes into the two metal oxides. Chris Smith John Emsley unlocking the secrets of element number 40, zirconium.

And you can find out some more about John's favourite elements in a series he has written for the RSC's Education in Chemistry which is online at rsc.org/education . Next time on Chemistry in its Element, life's a gas with Mark Peplow. Mark Peplow Little did those humble cyanobacteria realize what they were doing when two and a half billion years ago, they started to build up their own reserves of energy-rich chemicals, by combining water and carbon dioxide. Powered by sunlight, they spent the next two billion years terraforming our entire planet with the waste product of their photosynthesis, a rather toxic gas called oxygen. Chris Smith So join us next week for a breath of fresh air and the story of oxygen. I'm Chris Smith, thanks for listening, see you next time. (Promo) Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com . There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements . (End promo) Zirconium Zirconium is considered to be non-toxic. Characteristics: Zirconium is a strong, malleable, ductile, lustrous, grayish-white metal.

When present in compounds, zirconium exists mostly in the oxidation state IV. Its oxide (ZrO2) is white, like many of its compounds. Zirconium is generally exceptionally resistant to corrosion. It is however rapidly attacked by hydrofluoric acid, even at low concentrations. In an oxygen atmosphere, finely divided Zirconium burns with the highest known temperature for a metal flame: 4460 oC.(4) Powdered zirconium can spontaneously ignite in air. Exposed surfaces of zirconium form a protective oxide layer. Zirconium tungstate (ZrW2O8) is an unusual substance: it shrinks when heated from near absolute zero to 780 oC(5). Uses of Zirconium Zirconium is very poor at absorbing neutrons. It is therefore useful in nuclear energy applications such as in the cladding (outer layer) of fuel rods through which it is important that neutrons can travel easily. Zirconium is used as to make surgical instruments and is used in steel alloys as a hardening agent.

As a result of its exceptional corrosion resistance, zirconium is used extensively in the chemical industry in corrosive environments where zirconium’s alloys can be found in pipes, fittings and heat exchangers. Zirconium is also used to make superconductive magnets. Zircon (zirconium silicate, ZrSiO4) is a natural gemstone and synthetic cubic zirconia (zirconium dioxide, ZrO2) is produced as a low-cost substitute for diamond. Zirconium based catalysts are used in amination, hydrogenation, isomerization and oxidation reactions. Lithium zirconate can be used to absorb carbon dioxide. The reaction is reversible so the carbon dioxide can be released in a location of choice and the lithium zirconate used again. This application may be useful in addressing environmental concerns about the release of carbon dioxide into the atmosphere.

Abundance and Isotopes Abundance earth’s crust: 165 parts per million by weight, 38 parts per million by moles Abundance solar system: 40 parts per billion by weight, 0.5 parts per billion by moles Cost, pure: $157 per 100g Cost, bulk: $16 per 100g Source: Its chief mineral is zircon (zirconium silicate, ZrSiO4). It is produced commercially by reduction of the chloride with magnesium in the Kroll process. Isotopes: Zirconium has 25 isotopes whose half-lives are known, with mass numbers 81 to 105. Naturally occurring zirconium is a mixture of five isotopes and they are found in the percentages shown: 90Zr (51.5%), 91Zr (11.2%), 92Zr (17.1%), 94Zr (17.4%) and 96Zr (2.8%). The most naturally abundant is 90Zr at 51.5%. References 1. Photo by Dschwen .

2. Mary Elvira Weeks, The Discovery of the Elements XI., Journal of Chemical Education., July 1932, p1231/2. 3. Edward Turner, Franklin Bache, Elements of Chemistry: Including the Recent Discoveries and Doctrines of the Science, 1830, John Grigg, p304/5. 4.Mary Eagleson, Concise Encyclopedia Chemistry, 1994, Walter de Gruyter, page 1199. 5. Allegheny Technologies Incorporated. Zirconium Tungstate . (pdf document). Cite this Page For online linking, please copy and paste one of the following: <a href="">Zirconium</a> or <a href="">Zirconium Element Facts</a> To cite this page in an academic document, please use the following MLA compliant citation: "Zirconium." Chemicool Periodic Table. Chemicool.com. 18 Oct. 2012. Web.

< Zirconium, Chemical Element - reaction, water, uses, elements, metal, number, name, symbol zir-KO-nee-um Discovery and naming Naturally occurring compounds of zirconium have been used by humans since before the birth of Christ. For example, St. John talks about the jacinth (or hyacinth) stone. He says it was one of the jewels found in the walls surrounding Jerusalem. The jacinth stone was the same mineral referred to by the Persians as zargun, meaning "gold-like" in Persian. Early chemists did not study the jacinth stone very carefully. They thought it was another form of alumina (aluminum oxide). Alumina was a well-known mineral at the time. In fact, it was not until Klaproth undertook the study of the jacinth stone that he realized it contained a new element. Klaproth at first referred to the stone as Jargon of Ceylon. When he knew that he had found a new element, he suggested the name zirconium for it. The material discovered by Klaproth was not a pure element.

Instead, it was a compound of zirconium and oxygen, zirconium oxide (ZrO 2 ). The pure metal was not produced until 1824 when Swedish chemist Jons Jakob Berzelius (1779-1848) made fairly pure zirconium. He made the metal by heating a mixture of potassium and potassium zirconium fluoride (ZrK 2 F 6 ): Physical properties Zirconium is a hard, grayish-white, shiny metal. Its surface often has a flaky-like appearance. It also occurs in the form of a black or bluish-black powder. It has a melting point of 1,857°C (3,375°F) and a boiling point of 3,577°C (6,471°F. Its density is 6.5 grams per cubic centimeter. Zirconium has one physical property of special importance: It is transparent to neutrons. Neutrons are tiny particles with no charge in the nucleus (center) of almost all atoms. Industrially, they are used to make nuclear fission reactions occur. Nuclear fission is the process in which large atoms break apart.

Large amounts of energy and smaller atoms are produced during fission. Fission reactions are used to provide the power behind nuclear weapons (such as the atomic bomb). They are also used to produce energy in a nuclear power plant. One of the difficult problems in building a nuclear power plant is selecting the right materials. Many metals capture neutrons that pass through them. The neutrons become part of the metal atoms and are no longer available to make fission reactions A zirconium sample. occur. An engineer needs to use materials in a power plant that are transparent to neutrons—that is, that allow neutrons to pass through them. Zirconium is one of the best of these metals. If zirconium is used to make the parts in a nuclear power plant, it will not remove neutrons from the fission reaction going on inside the plant. A special alloy of zirconium has been developed just for this purpose. It is called Zircaloy. The manufacture of Zircaloy accounts for 90 percent of the zirconium metal used in the world today. Chemical properties Zirconium is a fairly inactive element.

When exposed to air, it reacts with oxygen to form a thin film of zirconium oxide (ZrO 2 ). This film protects the metal from further corrosion (rusting). Zirconium does not react with most cold acids or with water. It does react with some acids that are very hot, however. Occurrence in nature Zirconium is a fairly common element in the Earth's crust. Its abundance is estimated to be 150 to 230 parts per million. That places it just below carbon and sulfur among elements occurring in the Earth's crust. The two most common ores of zirconium are zircon, or zirconium silicate (ZrSiO 4 ); and baddeleyite, or zirconia or zirconium oxide (ZrO 2 ). The amount of zirconium produced in the United States is not reported. That information is regarded as a trade secret. The largest suppliers of zirconium minerals in the world are Australia and South Africa. These two countries produce about 85 percent of the world's zirconium.

Isotopes There are five naturally occurring isotopes of zirconium: zirconium-90, zirconium-91, zirconium-92, zirconium-94, and zirconium-96. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. About a dozen radioactive isotopes of zirconium are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. No radioactive isotope of zirconium has any important practical application. Extraction Zirconium ores are first converted to zirconium tetrachloride (ZrCl 4 ).

This compound is then mixed with magnesium metal at high temperature: Naturally occurring zircon is in demand as a gemstone. It is polished, cut, and used for jewelry and art. Uses Many zirconium alloys are available. They are used to make flash bulbs, rayon spinnerets (the nozzles from which liquid rayon is released), lamp filaments, precision tools, and surgical instruments. These uses make up only a small amount of the Zirconium alloys are used to make concrete drill bits. metal produced, however, compared to its application in nuclear power plants. Compounds About 95 percent of all zirconium produced is converted into a compound before being used. The two most common compounds made are zircon (zirconium silicate) and zirconia (zirconium oxide). Naturally occurring zircon is in demand as a gemstone. It is polished, cut, and used for jewelry and art. Natural zircon often includes uranium, thorium, and other radioactive elements. The presence of these elements often gives a zircon a special brilliance and fire-like quality, resembling fine diamonds. Zircon has other properties that make it desirable in industrial applications. For example, it is an excellent refractory material.

A refractory is a material that does not conduct heat well. It is able to withstand very high temperatures without cracking or breaking down. Zircon is used to make the foundry molds used to make metal pieces of all shapes. Molten metal is poured into the mold. When it cools, it is removed from the mold. The use of zircon in a refractory mold produces a smooth surface on the metal. Zircon is also used to make bricks in high-temperature furnaces and ovens. These furnaces and ovens are used to work with molten metals. Zircon bricks are ideal for such ovens because they reflect heat and are not destroyed by high temperatures. Both zircon and zirconia are used as abrasives. An abrasive is a powdery material used to grind or polish other materials. Another important use of zircon and zirconia is in making objects opaque. Opaque means that light is not able to pass through. Suppose a person wants to make a glaze for pottery that looks completely white. The glaze must reflect all light that strikes it and not let any light through. Adding zircon or zirconia to the glaze will achieve this result. Zirconium can cause skin irritation.

Deodorant products containing zirconium have been found to produce skin rashes. Health effects Zirconium is regarded as relatively safe. Some studies have shown that it can cause skin irritation, however. Deodorant products containing zirconium have been found to produce skin rashes. Also read article about Zirconium from Wikipedia User Contributions: Zirconium»compounds information [WebElements Periodic Table] Element News Zirconium: compounds information This section lists some binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and some other compounds of zirconium. For each compound, a formal oxidation number for zirconium is given, but the usefulness of this number is limited for p-block elements in particular. Based upon that oxidation number, an electronic configuration is also given but note that for more exotic compounds you should view this as a guide only. The term hydride is used in a generic sense to indicate compounds of the type MxHy and not necessarily to indicate that any compounds listed behave chemically as hydrides. In compounds of zirconium (where known), the most common oxidation numbers of zirconium are: 4.

Hydrides The term hydride is used to indicate compounds of the type MxHy and not necessarily to indicate that any compounds listed behave as hydrides chemically. Zircon - Varieties,Formation,Sources,Properties,Test,Value Zircon Valuation of zircon Many gem species have certain varieties that appear on the market only after they have been treated in some way to make them more attractive or saleable than in their natural state. Zircon (pronounced ZUR-conn) is a species that would undoubtedly be little known to the modern jeweler, if heat treatment were not used to convert the rather dull, natural stones into colors that are virtually unknown in nature. To be sure, one occasionally sees yellow-brown, yellow-green and cloudy dark-green stones that are probably untreated. However, their use in jewelry is very restricted and would be considered by most jewelers to be of interest only to avid collectors, jewelers are usually acquainted only with the heat-treated colorless and blue stones. Both blue and colorless stones occur naturally, but at present they are not found in sufficient quantity, and rarely in good enough quality, for commercial purposes.

Actually, natural colorless zircons, as well as the heat-treated colorless stones, have been known for years. More than one hundred years ago, authors mentioned colorless zircons as possible substitutes for diamond. It was not until after the turn of the present century, however, that this gem mineral gradually became popular, when material discovered in the Mongka district, Indo-China (now Cambodia), was found to change to blue when heat treated. This was not true of material from any of the previously known deposits. Similar material was discovered later in Siam (now Thailand). About 1920, several dealers recognized the possibilities of zircon, and they financed a number of cutting plants in the Orient to cut stones to their specifications. The result was the popular modified brilliant cut that has been used for the majority of zircons since that time. Although Ceylon was the first important source of both naturally colored and colorless stones, it was not known for blue zircons. For at least four hundred years, the colorless stones were known as "Matara" or "Matura diamonds," from a district of that name in Ceylon.

Two descriptive terms have been associated with the name zircon, neither of which is very specific, and today their use is diminishing. HYACINTH, or JACINTH, has been used for reddish-brown natural zircon (as well as for hessonite garnet), and JARGOON has been used for pale yellow to colorless stones from Ceylon. The name zircon is of doubtful origin. It may have come to us through the French from the Arabic "zarkum" meaning "cinnabar" or "vermilion" or from the Persian "zargun" meaning "gold colored". Both could allude to the color of natural crystals, although the latter would seem a better description. The word zircon was first used by Weiner in 1783 for crystals from Ceylon. Jargoon (or, as it is sometimes spelled, jargon) probably has the same origin as zircon. Hyacinth was the name of a youth in Greek mythology who was slain; the wild hyacinth flower supposedly sprang from his spilled blood. Since wild hyacinth flowers in Greece are blue to violet blue.

Pliny, in the first century A.D., compared the stone hyacinth with amethyst. Other ancient writers in alluding to hyacinth are surely describing blue to violet sapphires. It is recommended that zircons should be described by their color, rather than by specific variety names. Thus, we have white for colorless, blue, orange, brown, red, green, and yellow zircons. It can be seen by this that the range of color includes all but the violet portion of the spectrum, although long exposure to X-rays or electron bombardment has been known to produce a temporary violet or purple color in some stones. In addition to being far from clear cut in history and terminology, zircon is not simple mineralogically. It is recognized that there are three more or less distinct types of this mineral. These types have been given several, designations, such as alpha, beta and gamma; for clarity, however, we will refer to them as high, medium and low types, because their properties vary in this way. In this regard, zircon is unique among gem minerals.

Although the chemical composition, zirconium silicate, is fairly simple, certain alterations of the high type account for lower properties in the medium and low types. The three types were first described in 1903. In addition to the elements zirconium, silicon and oxygen, which make up the chemical formula of zircon, small amounts of many other elements are usually present; e.g., zinc, calcium, iron, copper, titanium, radioactive elements such as uranium and thorium, and rare earths. The metallic elements hafnium (named for Hafnia, an old name for Copenhagen) was first isolated in 1922 from a Norwegian zircon. In certain areas, beach sands contain a significant proportion of zircon grains. In some sands, the proportion is great enough to make mining feasible. In Florida and Australia, zircon is separated from sand by gravity concentration methods. The ore is used in the manufacture of refractories, high-temperature industrial ceramics, and chemicals, it is also used as foundry sand and as the source of the metal zirconium.

Types of Zircon High-Type Zircon By far the most important type of zircon to the trade is the high-property type from Cambodia and Thailand, where it occurs as waterworn pebbles or stones with traces of tetragonal crystal forms in colors ranging from pale yellow brown to deep red-brown. When heated, colorless, blue and golden-yellow colors are produced. However, it has been ascertained that stones from different mines will produce different proportions of these colors. The heat treatment is carried out by placing about one kilogram (5000 carats) of pebbles and crystals in a closed fireclay crucible and surrounding the crucible with coals in a primitive stove, much like the ones used in many Bangkok households. The stoves are fitted with suitable apertures and grates but no pyrometers (thermometers) are used. A funnel-like stovepipe or another stove on top of the first can be added to increase the draught, if needed the first heating in a reducing atmosphere turns many of the stones an acceptable blue color, although the proportion of worthless stones is said to be approximately 70%.

Pale but clear stones are returned to the stove a second time in a perforated crucible, thus producing an oxidizing atmosphere, and many are changed to colorless, yellow, orange, etc. Further heat treatment may be employed, and some stones may thus have been heated five or six times, or even more. Several authors have stated that complicated use of of chemicals was needed along with the heat treatment to produce white stones. Experiments in Western laboratories and more accurate information from visitors to the cutting areas discount the need for chemicals. In fact, one can demonstrate the effect of heat on a brown crystal by holding it in the flame of a blowpipe, gas jet, or even an alcohol lamp. Within five minutes a crystal of a carat or two will become colorless upon cooling. Similarly, a pale-blue stone might turn a darker blue with the same treatment, although since the heating is difficult to control, it may become greenish or lose all color. Thus, the experiment is not suggested as a remedy for changing faded stones to their original saleable. Some investigators have indicated that a reducing atmosphere along will produce a blue color. The reason for the apparent discrepancy seems to be due to the fact that stones from different mines behave differently.

Further, it has been found that some of the mines have produced much better colorless stones and stones that are less apt to fade or revert toward the original color. One mine was famed for its colorless stones, which were never troublesome in this manner. This mine is depleted. This perhaps explains part of the reason why some shipments of zircons give dealers in this country little trouble and why others tend to revert, even when kept in the darkness of a safe. The rough stones are generally purchased by dealers who take them to Bangkok, where native lapidaries heat, cut and polish them with remarkable skill. Many of the more conscientious dealers subject the cut stones to strong sunlight for at least forty-eight hours in a well-ventilated place before shipment. The stones that are prone to change color are detected and rejected or reheated. Unfortunately, other dealers are not as careful. This was particularly true during the gem starved post World War II period, with the result that many zircons changed for the worse after delivery in the United States or Europe. The colors available in Bangkok include blue and colorless as the most important, with golden yellow and orange stones occasionally and garnet-red stones rarely.

The unheated stones are seldom cut, even though their color may be a rather attractive dark red-brown to light brown. Although many suggestions have been made regarding the causes for the color change and how to restore the desired color to the occasional stone that begins to revert toward its original appearance, it is fairly well proven that a zircon that once begins to alter will again do so regardless of how often the color is restored. Many importing firms in the United States grade their zircons carefully for color and store them for a period of time, regarding them occasionally and discarding those that have changed. After a year, those stones that are apparently color fast are sold, since the firms consider they have done their best to protect their customers. In addition to changing the color, the heat treatment that most zircons undergo before entering the jewelry trade also alters the structure somewhat; as a result, they tend to chip or pit easily at facet junctions, even though they are actually somewhat harder than quartz. This accounts for the typical abraded facet junctions that are so common to zircons, even when they are handled and worn with care.

High-type (or, as it is sometimes called, normal type) zircon has a high specific gravity, varying from approximately 4.6 to 4.8; a high refractive index of approximately 1.90-1.94 to 1.95-2.01, with a consequent birefringence near .06; dispersion factor that averages .038 (diamond 0.44), explaining why the colorless stone is an effective-diamond substitute; and a hardness of about 7 1/2. It is found in wellformed tetragonal crystals in many parts of the world, but only a few areas produce gem quality stones, and these are mostly water worn pebbles. Low-Type Zircon Low-type zircon occurs in gem quality only in Ceylon and only as rolled pebbles in the gem gravels without any trace of crystal faces. The color is usually green and usually tends to be a grayish to yellow-green with a somewhat cloudy texture; brown and orange stones are also known to occur.

The stones are rarely sold as zircon in Ceylon, but usually are offered in parcels marked "tourmaline" (a word from the Singhalese meaning "mixed precious stones"), or sold as "green sapphires" to unsuspecting tourists. Low zircon has been found to be composed of amorphous silica (SiO2) and amorphous or alternatively microcrystalline zirconia (ZrO2). Heating to 1450°C, usually does not alter it, beyond perhaps driving off a brownish cast in some stones. Overheating may change the stone to a worthless opaque condition. The properties seem to remain unchanged after heating. The refractive index varies from approximately 1.78 to 1.82, with just measurable birefringence. The hardness is about 6 and the specific gravity is 3.9 to 4.1. Dispersion is nil. Intermediate-Type Zircon Gem material that is recognized as intermediate-type zircon comes only from Ceylon. It is found only as rolled pebbles in shades of greenish yellow to yellow-green, brownish green and greenish brown.

As the name indicates, the specific gravity, refractive index and birefringence vary between those of the high and low types. Stones that approach the high type in specific gravity have the higher R.I. and birefringence and a more yellowish or brownish cast, instead of the purer green. The most interesting characteristic of these intermediate stones is that heat treatment at about 1450°C causes the properties to increase toward those of the high type, some stones actually gaining the optical and physical properties of the high type. Since the bountiful supply of zircons from Cambodia (particularly the heat-treated blue stones) have come on the market, not much heat treatment is carried out in Ceylon, where only a muddy to cloudy-white color results from heating the intermediate-type stones. The occasional high-type brown stones may turn a fine orange color and resemble hessonite garnet. The untreated intermediate stones that do reach the market are usually sold under some other name or are sometimes imported for collectors. Occasionally, good yellow stones come on the market and are sometimes inadvertently sold as "golden sapphires".

It is now thought that the presence of radioactive elements such as uranium and thorium in zircon crystals at the time of formation account for the atomic derangement resulting in the breakdown of the normal structure into the nearly amorphous low type of zircon. This breakdown is fairly common in other minerals containing radioactive elements such as uranium ores, and is due to the incessant bombardment during millions of years by alpha particles emitted at great speed from the slowly dis-integrating radio active elements. Sorby, in the last century, along with Sir Arthur Church, was one of the first to study zircon under the spectroscope. In 1868, he examined some stones and detected such a spectacular absorption spectrum that he suspected a new element and proposed the name "jargonium" for it. (Ninety years previously, zirconium had been isolated and named for zircon by Klaproth.) Later, it was proven that uranium was responsible for the striking absorption spectrum seen in some zircons. Under the influence of heat, the process of disintegration is reversed in the intermediate stones, but it is assumed that too much radiation damage has been done in most low-type stones for heating to be successful in restoring the normal crystal structure.

Why the colors change or just what causes the color in the first place is not agreed upon by scientists, although as we have seen, zircon frequently contains impurities, several of which might one day be discovered to be causative factors. It should be noted that there is no dangerous radiation from zircons today, and the subject of radioactivity should probably not be mentioned to a radiation conscious public. An interesting occurrence in support of the radiation-damage explanation for the intermediate and low types of zircon is the occasional discovery of a crystal in which both types occur in combination. A cut stone from Ceylon, described in 1952, was half green (low type) and half orangey yellow (intermediate type). All properties that could be measured showed that the stone was indeed half low and half intermediate zircon. The assumption is that the crystal originally was formed with one half containing more radioactive elements than the other. Formation of Zircon As a mineral, zircon is not rare. It is a common constituent of igneous rocks, such as syenite and granite, and of many metamorphic rocks, such as crystalline limestone and gneiss.

In Norway, syenite is so rich in zircon that the rock has been given a type name of zircon-syenite . However, these rocks are not mined for either gem zircon or metallic zirconium. Because of the insolubility of zircon crystals and their toughness , compared to many other rock-forming minerals, they survive the breakdown of parent rocks and are therefore prominent constituents of gem bearing gravels in several areas of the world. These gravels are the only commercial source of gem zircons, since no source in matrix has ever been profitable to mine. Sources of Zircon Ceylon From ancient times the island of Ceylon has been the source of many colored stones. Zircon is one of them.

Here it is found in the gem gravels with corundum, chrysoberyl, spinel, topaz, garnet (hessonite, almandite and rhodolite), tourmaline, quartz (rock crystal, amethyst and pale citrine), orthoclase moonstone, sphene, iolite, fibrolite, andalusite, diopside, rutile, apatite, sinhalite, komerupine and the exceedingly rare taaffeite. The recovery methods used are very primitive. The mining is entirely in the hands of the Singhalese. Usually, an owner hires workers for their food and housing, plus a share of any yield beyond their cost to him. If the pay gravels are at or near the surface, mining is simple. An area of about four feet square, making room for two or three miners to work, is worked to the bottom of the pay zone, but this is not undertaken until the appropriate ceremonies beseeching the gods for success are conducted. This kind of mining is successful only if the gem bearing layer, locally called "illam," is near the surface.

If the gravel is much deeper, the pits are dug about six feet square and from ten to twenty feet deep or even more. Unless the overburden is very strongly consolidated, the pit walls must be shored to prevent caveins. If a number of pits are dug close together, tunnels may be constructed connecting them. One disadvantage of a deep pit is that it is likely to be below the water table in most of Ceylon. This water is bailed out by an especially constructed winch with a number of buckets attached to a connecting rope with stone counterweight. The miners dig until they encounter either a blackish rock, known as "ralu ratta," or a rocky gravel of whitish color called "thiruvana". This is an indication to the miner that the next layer must contain gems he is near the illam. If they encounter a layer of clay after removing the illam with their baskets and the winch, they do not dig any farther, because in do so has proven fruitless. When no more illam is obtainable, the owner chooses an auspicious day for the washing and sorting. Until this time, the heap of gravel is covered with leaves and well guarded.

If the mine is near a river, the gem gravels are transferred to its bank and washed in special conical baskets. The lighter materials is swirled off and the heavier contents are then examined. In other areas, trenches are dug and filled with water for the washing process. Zircon is the densest gemstone recovered. The mine owner is always on the spot, since the miners do the washing and sometimes cannot resist the temptation to hide a good stone. Occasionally, the illam is found in a stream bed; in this case, the stream is dammed, except for about five feet in the middle, where a log is placed to control the water level. Using a long rake like implement, the miners pull the gravels toward the log until the Mem layer is reached. Then, either by wading in with baskets or by diving, the illam is collected and washed on the spot. Mining is conducted mostly during the dry season, which is from March to November. At other times, the heavy rains fill the pits and trenches, making mining impossible.

The mining is not done for zircon alone, for zircon, as mentioned previously, is only one of the many gem minerals found, several of which are more valuable to the miners and owners. Certain areas and mines in Ceylon are known for the rather greater concentration of one gem mineral than another. Chrysoberyl cat's eye, for example, is more prevalent in one area than in another, and the same is true with certain sapphires and moonstones. No one area, however, is particularly noted for zircon. The most profitable mining centers are near the town of Ratnapura, near the southeast end of the island. Only the actual mining is in the hands of the native Singhalese; the gem trade in Ceylon is carried on exclusively by Moors, ancestors of whom reached Ceylon centuries ago. Moorish lapidaries in the area of the mines cut many of the stones, which are then sold to dealers in Colombo. As was previously mentioned, the zircons among them are seldom sold as such, but are relegated to nixed parcels that are sold for little money, in as much as neither the cutting nor the colors of most are particularly desirable.

Cambodia As stated before, the most important source of zircon to the trade is Cambodia, particularly in the Kha district, east of the Mekong River, in an area near the border between Cambodia and South Vietnam (indicated by the solid-black circle on the accompanying map). Mining methods are essentially the same as those in Ceylon, since in both areas the miners are searching for layers of subsurface alluvial gravel in which heavy minerals are concentrated. Pits must be dug to reach the gem gravels, and these are seldom more than eight to ten feet deep. One difficulty in some areas is the relatively drier climate, although along the banks of the rivers and streams, water is available for the washing. It is claimed that most of the mining is done by Burmese hill people, who discovered the deposits late in the last century. One difference between the mines of Ceylon and those of the Cambodia-Thailand region is that in the former many different species and varieties are found, whereas, except for one mine in Cambodia, only zircon is commercially important. The Kha mines are very remote and are seldom visited by Westerners. Those who brave the trip say they can buy rough more advantageously in Bangkok than at the mines.

The Ceylon mines are readily accessible by train from Colombo. Burma Greenish-yellow to yellow-green zircons are found occasionally in the Burmese ruby mines. No extensive trade in zircons is carried on here, and those discovered are usually sold without treatment or, at times, without identification. These stones are unusual for their striking absorption spectrum in the spectroscope, where as many as forty or more lines may be seen. Miscellaneous Sources No other commercial source of zircon exists, although cutable stones have been found in France as brilliant red crystals at Espaly-Saint-Marcel; in New South Wales, AusNo other commercial source of zircon exists, although cutable stones have been found in France as brilliant red crystals at Espaly-Saint-Marcel; in New South Wales, Australia; with diamond in kimberlite in South Africa; in Madagascar; in Russia; Mention should also be made of the gigantic red crystals that have been found in Canada in Renfrew county, Ontario. Some of these have weighed up to fifteen pounds and measured more than twelve inches long, although clear areas would cut stones little larger than one carat in weight.

Fashioning of Zircon Compared with most colored stones cut in the Orient, zircon is the only species for which standards were established to control cutting quality at the time the material was first promoted. As a result, dealers today would not consider buying poorly cut stones. This factor has been largely responsible for the success of zircon in jewelry. The cuts employed are very much like those for diamond. The most successful is the round brilliant, because, as with diamond, it allows the high refractive index and dispersion to be manifested as brilliancy and fire. The attempts to popularize marquise and other fancy cuts have not been successful, since the stones seem dull compared with diamond, although small baguettes cut fuller than diamond baguettes are quite effective. Formerly, a type of cut recognized as the "zircon cut" was used extensively. This style utilized an extra eight facets around the culet. Today, examination of newly imported lots usually fails to disclose examples of this method of fashioning; instead, the standard 57-facet brilliant is used (no culet), especially for the blue and colorless stones.

In general, in order to display the dispersion to best advantage, the crown of brilliant cut zircons is heavier than most brilliant cut diamonds, particularly since "spreading" has been so much in evidence with diamond in recent years. In Ceylon, the usual "Ceylon" style of cutting is generally employed, which makes the best use of the material for weight but is woefully lacking in symmetry and brilliancy. One may therefore see cushion antique cuts, off-shaped tear drops, and unclassified off shapes. Sometimes the stones are deeper than they are wide. Thus, matching stones is impossible without re-cutting. Standard mountings that are used for other inexpensive stones can rarely be used. For this reason, zircon in Ceylon suffers in popularity from the hidebound cutting traditions even more than the more valuable species from Ceylon, which are cut primarily to save weight too. Re-cut in this country or Europe, some of Ceylon's green and golden yellow stones are very attractive. Good heat-treated rough material for cutting in this country or Europe is very difficult for lapidaries to obtain. One rarely sees crystals that are worth cutting, even if it would pay financially to cut them here or in Europe.

When parcels of rough white or blue material are seen, close inspection usually discloses that the stones are evidently rejects from Thailand, being either too cloudy or having inclusions that could not be removed economically. Parcels of low-quality mixed stones may be purchased occasionally from Ceylon. Usually, a high percentage of the stones will be medium-and low-type zircon, together with brown chrysoberyl, dark sapphire and spinel, and sometimes the rare sinhalite and komerupine. In Bangkok, the cutting of zircons is not concentrated in a few large shops, as the more or less standardized cutting would suggest; Instead, the cutting takes place in many shops having a few polishing wheels each. Therefore, the methods of working the rough are not necessarily standardized, just as the heating is not carried out under identical conditions. The rough stones are seldom large enough to require sawing. They rare roughed out on vertical carborundum hand wheels, then smoothed on fine-grit horizontal carborundum wheels. Facets are cut and polished on steel or iron laps with bort as the abrasive.

Lapidary work on zircon in this country is confined largely to re-polishing worn stones (if they are large enough to warrant the cost) or re-cutting off-shaped Ceylon stones. Care must be exercised during the sawing operation, because zircon tends to clog the diamond saw. Facet grinding may be done on a copper lap with diamond powder or on a lead wheel with carborundum powder. The proportions usually recommended are one-third above the girdle and two-thirds below. An effective cut is produced when the main crown facets have an angle with the girdle of about 40° and the inclination of the pavilion facets is at 41°. Ideal diamond angles are 341/2° for the main crown facets and 40 3/4° for the pavilion facets. Examination of a number of commercially cut zircons from Bangkok indicates at least as good adherence to good proportions as one finds in most diamonds. Polishing is usually accomplished most satisfactorily with Linde A powder. Some zircons, especially the low type, may present zones of uneven hardness.

With such stones, polishing may proceed normally with damp polishing Powder; however, when the soft zones are encountered, the powder should be permitted to become almost dry and the lap speed should be reduced considerably. Test and Identification of Zircon Since zircon occurs in a wide range of colors, it may be confused with almost any transparent to semitransparent gemstone with a similar color. To the casual observer, a well-cut and scrupulously clean zircon may be confused with a diamond of the same color. Since zircons that are able to masquerade as diamonds will be either the high or medium type, the most obvious characteristic is the apparent doubling of facet junctions, inclusions, scratches or dirt observed through the stone. Since the amount of doubling depends on the orientation of a cut stone, it may be necessary to make observations in several directions. Because diamond is singly refractive, the observance of any doubling eliminates diamond as a possibility. Of the other transparent stones that might be confused with high or medium zircon on the basis of appearance alone, all but the rare gemstone sphene and synthetic rutile may be eliminated on the basis of double refraction, S.G.

(for unmounted stones) and R.I., which is higher than the refractometer scale (1.81). The S.G. of sphene is approximately 3.52, which is lower than for any zircon. The easy parting and cleavage of sphene is observed frequently as incipient cracks in a cut stone. The absorption spectrum of a zircon that resembles sphene would almost certainly separate the stones. Synthetic rutile displays such a high degree of dispersion that few persons are likely to confuse it with zircon. Also, the strong doubling in some directions in synthetic rutile is far greater than zircon and would be unmistakable to anyone who has observed it in even a few zircons. Stones represented as synthetic zircon are almost sure to be synthetic spinel or, rarely, synthetic sapphire. No difficulty in identifying them should occur, if recourse is had to the refractometer and polariscope. The low-type green zircon can be confused by sight alone with various green stones, such as tourmaline, diopside, demantoid garnet, peridot and sapphire. Again, the refractometer and polariscope will suffice to make identification positive in almost every case.

Green sapphire may pose a problem. Although corundum and synthetic corundum are amazingly consistent in R.I., averaging as they do 1.762-1.770, there are two exceptions: the very dark-red synthetic that is used to imitate almandite garnet, and natural green sapphire. Both may read as high as 1.772-1.780 in R.I. Rarely, low zircon may descend to 1.78; however, at that level, there is no visible birefringence in zircon. Since it may have the same S.G. and similar appearing inclusions, it can be seen that instrument tests must be made with care. Of course, the hardness of the zircon is considerably less, but a less drastic test than hardness is to observe the absorption spectrum, which, as we have seen, is distinctive for this type. Occasionally, backed rose-cut colorless zircons appear in Indian (Hindu) jewelry. They may be interspersed with rose-cut diamonds and the characteristic enamel and colored stones that are so typical of this kind of jewelry. Since R.I. and S.G.

cannot be taken, the clue is to observe the stones under high magnification for double refraction. If doubling is seen in these small, flat stones, it is fairly certain that they are zircon, since no other colorless doubly refractive stone in such small sizes will show pronounced doubling. Because blue zircon may have the hue of good aquamarine (but the latter are hard to find in good color in small sizes), one occasionally encounters aquamarines set with matching small zircons. Again, the observation of strong doubling in small stones is virtually conclusive, for no other aquamarine blue stone shows such strong doubling in such small sizes. In the mixed parcels of Ceylon gems, two stones that are frequently confused on sight are brownish-yellow zircons and sinhalite, both of which show a noticeable doubling of back facet junctions. One dealer, upon learning of the "nevi" stone, sinhalite, bought parcels of Ceylon zircons abroad for about $20 per carat. There were nine sinhalites about of thirty-four stones he thus obtained from unsuspecting sellers. He needed the sinhalites, since he has a large clientele of collectors.

Valuation of zircon Color Of the two color varieties of zircon that are the most popular, colorless and fine blue, the latter is the most valuable. This color is found in no other gemstone, except, ironically, some of the more recent colors of diamond produced experimentally by atomic bombardment. Blue zircons should be examined by daylight to determine if the blue is pure and not modified by a yellowish cast, particularly in one dichroic direction. If a yellowish cast is present, it indicates a stone that may be reverting to its original color. Although the blue of fine zircons is usually slightly greenish, some approach the color of fine aquamarine; these bring the highest prices, if the color is evenly distributed. Colorless zircons should be as transparent as a fine diamond and free from any grayish or brownish cast. Although the stones with a brownish cast may be reheated to restore colorlessness and fine transparently, the change is usually short lived. Some actually seem to display greater dispersion and a higher luster for a few hours after heating, but return to the more normal condition afterwards. Other colors of zircons should be as transparent as the color will allow.

Purity of color, evenness, and clarity of texture should be observed. Dull stones of low intensity or poor brilliancy have little appeal and are of little value. Even the better fancy colors (i.e., those other than blue and colorless) have had little demand, due to the lack of appreciation on the part of both buyer and seller. The fine flame-colored stones seem to have enough appeal to sell readily, however. Clarity Flawless or nearly flawless zircons have been available in sufficient quantities so that there has been little demand for flawed material, specially in colorless and blue stones. These should have no blemishes, at least when judged with the unaided eye. Stones should be observed for the characteristic abrasions along facet junctions. Zircons that have been jumbled together in papers without being wrapped individually will show the abrasions. If visible to the unaided eye, the stones should be rejected or Tepolished, if the value warrants. It is well to reject stones that have a cloudy texture, regardless of their color. Cut The beauty of zircons is primarily the result of high R.I. and dispersion, together with the adamantine luster of well- polished stones.

The cutters in Bangkok seem to understand this, since they keep the cutting fairly well standardized. To attempt to "swindle" the stones to get more from the rough at the expense of beauty, as is so commonly done with diamond, would only defeat their purpose in cutting. However, blue and colorless zircons with flat crowns or other departures from the ideal are occasionally encountered, and they should be judged less valuable than well-made stones. In a multi- stone piece of jewelry, the stones should be cut to about the same proportions, so that the design is pleasing and there are no "dead" stones. With cuts other than the brilliant, attention should be paid to the over-all brilliancy. If , as is seen in marquise cuts, particularly, there is a large dead area in the center, the stone will not give satisfaction when worn. This is true particularly in ring stones, where dirt frequently collects on the back of stones and shows through. This, in fact, is one disadvantage of even the best zircon when compared with diamond, and is much worse for a stone with a dead area.

Ceylon-cut stones are usually judged on the basis of their value after re-cutting to proper proportions, although an attractive stone may occasionally be encountered. Orientation Because of the high birefringence of high-type zircon, stones with the optic axis parallel to the table, or nearly so, will show a fuzziness caused by the doubling of the back facets. This is particularly true in larger sizes. If this is to be avoided, the stones should be cut with the optic axis perpendicular to the table. To judge this factor, the stones should be observed directly through the table. Those with no doubling in this direction are more attractive, although they may not necessarily command a better price, since color and other factors must also be considered. Orientation also affects the color of blue stones, because some will show a desirable blue across one area of the stone alternating with distinctly lighter blue or, worse, with a yellowish blue. The color should be as even as possible, although some slight variation is almost unavoidable. As with the corundum gems, fortunately, the best blue color is seen parallel to the optic axis.

Therefore, when the stones are cut so that the optic axis is at right angles to the table, the best possible color will be visible, and the fuzziness noted above will be at a minimum. Size Blue and colorless zircons are usually available in sizes from a few points in weight to nine or ten carats. At one time prior to World War II, 15 to 25 carat blue stones were available from many suppliers. Since the War, stones in excess of ten carats have been very scarce, especially in truly fine colors. Links

Question: What element, with zirconium, forms the compound zirconia, which is used to make synthetic diamonds?
Answer: Oxygen