Zircon And Allied Minerals

Zirconium Silicate
Zr.SiO₄

Of the several zirconium minerals known only two, viz., zircon and baddeleyite are of commercial importance.

The History Says

During the Middle Ages, zircon was believed to contain remedial power, protecting the wearer from diseases and banishing insomnia. The name "zircon" is believed to have derived from the Arabic words, "zar", meaning gold, and "gun", meaning color. It was discovered in Germany in 1789 by Martin Klaproth.

The Present Scenario

Thailand and Cambodia are the world's major suppliers of zircon with large deposits near the border of the two countries. Vietnam, Burma, Sri Lanka and Africa also provide a large supply of these marvelous gemstones to the world market.

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ZIRCON is the chief mineral of zirconium, a versatile metal. The zircon is a common accessory mineral of igneous rocks, like syenite, granite and diorite. Economic deposits are, however, concentrated along the beach sands and found in association with ilmenite, rutile etc. as it occurs in the beach sands of Australia, USA, South Africa, West Africa and India.

Zircon invariably contains hafnium. There are fourteen zirconium minerals of some importance and all of them contain hafnium. It has been observed that the hafnium content in the minerals originating from syenite rock is less than in those occuring in granite.

Hardness	Associated Minerals	Chemical/Typical composition	Colour	characteristics	Luster	Field Indicators
7.5	albite biotite garnets xenotime monazite	ZrO2 ......67.2% SiO2 ......32.8%	Brown Red Yellow Green Blue Black colorless	sometimes fluorescent and darker crystals may be radioactive due to impurities of rare earth elements.	adamantine	crystal habit, hardness, luster and density

Note : Zircon is the birthstone of the month of December.

Important Uses

Zircon

• Ceramics
• Chemicals
• Foundry
• Opacifiers
• Refractories
• Welding rod coatings
• Zirconia

Zirconium and Hafnium

• Chemical piping in corrosive environments
• Heat exchangers
• Nuclear
• Specialty alloys
• Superalloys

Appearance

Zircon, a naturally occurring gemstone, has colorless, yellow, orange, red, blue, brown and green varieties. Zircon, by it's name, is sometimes confused with cubic zirconia ("CZ"), which is synthetic. In addition, both have been used as diamond substitutes. Zircon has a high refractive index which is responsible for it's diamond like appearance. Zircon can be distinguished from diamond by it's double refraction and by wear and tear of it's edges, as compared to diamond which is very much harder.

Enhancements

Green and brown colors of zircon are not enhanced. Yellow zircon is rarely heat treated to improve color. Blue, red and colorless are always heat treated brownish crystals to produce these colors.

Industrial Applications

Zircon, baddeleyite or manufactured zirconia are all useful refractory materials. They are valued for the preparation of special moulds and refractory bricks. High-grade zircon melts at about 2190ºC, softens between 1600ºC and 1800ºC and shows little shrinkage upto 1750ºC. Zircon exhibits many characteristics that make it very suitable for super refractory purposes. In addition to a high melting point it was very low thermal expansion and good resistance to abrasion. Zircon is used when acidic refractory is required while zirconia refractories are considered to be basic. A cheaper type of zircon-refractory is prepared with mixing zircon with alumina. It is reported to have refractory properties as good as those of zircon. At high temperatures the following reaction takes place:

2ZrSiZO₄ + 3Al₂O₃ = 2ZrO₂ + 3Al₂O₃. 2SiO₂

The dissociation of zircon starts at 1400ºC and at about 1600ºC a complete reaction takes place forming a stable product of zirconia and mullite. The high grade zircon sand is largely used in foundry as mould. It does not wet the molten metal, thus giving a better and smoother surface to the casting. It is estimated that about 75% of the total world zircon production is used as moulding sand and in the manufacture of refractory bricks, zirconium compounds and ceramics. Only 25% is used for the extraction of metal or in the manufacture of alloys.

Prepared zirconia and also zircon are extensively used in the glass and ceramic industry for opacifying enamels, porcelain and glazes.

Zircon sands bonded into bricks are also used in large quantities as refractory bricks in glass and aluminium industries. Zircon has special properties of resistance to spalling and wetting by glass and aluminium which makes it suitable for the above purpose. Finely powdered zircon and zirconia are used as an abrasive in polishing optical glasses.

World Resources

Australia
This country is the leading producer and exporter of zircon which is obtained as byproduct of rutile recovery from the beach-sands. The largest concentration of such sands is found on the eastern coast, extending over 160 km, in Queensland. Concentration of such sands is observed in the Byoon Bay, New Brighton-Cudgera, Cudgen and Currimbin-Southport area and on North Stradbroke island. It is reported that on this island the heavy sands contain about 25% zircon. Deposits are worked by several companies. Australian deposits are wide-spread and quite large.

USA
The source of zircon in this country is Florida beach and Trail ridge. Production in Florida started in 1922 from the Pablo Beach area near Pdonta Vedra. The total heavy minerals in the beach of this area contain hardly 4 to 4.5%. The heavy mineral concentrates give 45% ilmenite, 14% zircon besides other minerals. Another area near Starke, Florida, was opened up in 1948.

One of the most important sources of zircon, rutile and ilmenite discovered in the USA lies in Trail ridge some 72 km inland formed in mid-Pleistocene time as a sands pit part of an ancient beach. It consists of a strip of ridge running for a distance of 40 km, ranging from 900 metres to 2400 metres in width with an average height of 45 metres. The average concentration of heavy minerals is about 3.9%. the percentage of zircon in the concentrate is 14%. The estimated reserves of heavy sands in this deposit are 21 million tons and the potential reserves of zircon are estimated at 2.5 million tons with 80% recovery. Production statistics of zircon in the USA are kept secret.

Brazil
The zircon minerals, like baddeleyite, orvillite (altered zircon) and zirkite, are mined from open pits in the Pocos de Caldas plateau in Mines Gerais.

West Africa
The beach-sand between Rufisque and the mouth of the Saloum river is reported to contain zircon.

Republic of South Africa
The beach-sands of Durban contain zircon which is mined. The reserves are extensive.

USSR
The known source of zirconium mineral is eudialyte, which is recovered from the apatite deposits in the Kola peninsula.

Ceylon
The beach-sands at Pulmoddai and Tirukkovil in eastern Ceylon contain about 25% of zircon.

Malayasia
An appreciable quantity of zircon is present in the alluvial tin deposits. It is reported that the Japanese produced 741 tons of zircon during the occupation.

India
The beach-sands of Kerala and adjoining Madras coasts contain an average 5 to 10% zircon. It is recovered from the tailings of ilmenite plants. The production of zircon in the country is controlled by the Atomic Energy Department, Government of India.