Zircon, Zirconium Silicate and silicate minerals all are rich sources of zirconium. It is a member of the nesosilicate group and is considered to be the main source of metal Zirconium. It is a precious gemstone that was discovered almost 2000 years ago. The diamond look-like crystal is often confused with zircon but it is actually cubic zirconia which is identified as a lower and cheaper version of the diamond. On the other hand, zircon is much softer as compared to diamond or cubic zirconia and are also available in several colours. The most common ones are white and blue.
What is Zircon? Where Does it Occur?
Zircon is a rich source of Zirconium metal and it belongs to the nesosilicate group. Zircon is chemically known as Zirconium Silicate and its chemical formula is ZrSiO[_{4}]. Zirconium is generally formed in melts of silicates and shows properties of high yield strength elements that are incompatible in their nature.
It has a crystal structure with a tetragonal crystal system. The empirical formula developed to indicate the range of substitutes in zircon is (Zr[_{1-y}], REE[_{y}]y)(SiO[_{4}])[_{1-x}](OH)[_{4x-y}].
Zircon is commonly found in the crust of the earth. Zirconium is widespread as an accessory mineral in felsic igneous rocks and in most granites. As because zircon is inert in nature to chemical reactions and is quite hard as well as sturdy, they are mostly found in sedimentation deposits, fairly often in detrital deposits as well as metamorphic rocks. It is a usual constituent of sands and thus occurs in beach sands in many parts of the world that include India, Australia, Brazil and Florida in particular. It is commonly found in Quebec in the form of large crystals and is a very important part of syenite present in Southern Norway.
Physical and Optical Properties of Zircon
The diagnostic feature of zirconium is its physical characteristics like the shape of the crystal, colour, hardness, lustre and specific gravity. Thus it is very important to acquire knowledge about various aspects of its physical properties for better identification.
Physical Properties of Zircon
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Crystallography |
Crystals usually show a first-order combination of prism and pyramid. So they are either tetragonal or ditetragonal-pyramidal |
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Composition |
Zirconium Silicate (ZrSiO[_{4}].ZrO[_{2}]) = 67.2% SiO[_{2}] = 32.8% |
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Chemical Classification |
Silicate |
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Colour |
Usually white, yellow, brown, red, blue-green, grey and also sometimes colourless |
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Specific Gravity |
4.6 to 4.7 |
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Lustre |
vetriousto adamantine but sometimes oily and greasy when metamict |
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Cleavage |
Imperfect |
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Mohs Scale Hardness |
7.5 |
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Tenacity |
Brittle |
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Crystal Habit |
Massive with irregular grains and tabular to prismatic crystals |
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Diaphaneity |
Translucent to Transparent |
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Twining |
At {101}. When crystals are shocked with meteorite impact, they show polysynthetic twins on {112}. |
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Facture |
Conchoidal to uneven |
Zircon has some very unique optical properties as well.
Optical Properties of Zircon
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Properties |
Values |
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Zircon Crystal System |
Tetragonal (4/m²/m²/m) |
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Crystal Habit |
Microscopic Crystals |
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Cleavage |
Poor{110}in prismatic and poor {111} in pyramidal |
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Streak |
White |
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Optic Sign |
Uniaxial (+) |
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Fluorescence |
Thermoluminescent, cathodoluminescent, may appear fluorescence under UV light |
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Optical Orientation |
Length slow |
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2V |
Not observed due to small crystal size |
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Refractive indices Omega = Epsilon = |
1.920 – 1.960 (1.924 – 1.934, natural non- metamict) 1.967-2.015 1.970 – 1.977 |
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Elongation |
Along C-axis |
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Max Birefringence |
0.036 – 0.065, (for non-metamict) 0.036 – 0.053 |
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Extinction |
In grain mount or parallel in longitudinal |
Application and Uses of Zircon
Zircon and its derivatives have a wide range of applications and use in many industries. The largest industry that uses zircon for a vast range of applications is the ceramic industry. About 54% of the total zircon produced worldwide is used in the form of finely grounded dust for industrial applications. Approximately 14% goes into the foundry industry in sand and casting and the rest 11-14% is used in refectory applications.
In the ceramic industry, most of the zirconium is used for manufacturing ceramic bodies, glazes, frits, enamels and pigments that are applied to traditional ceramics. It is also used in traditional ceramics as an opacifier in order to improve its whiteness and brightness. But 85% of zircon is used for manufacturing tiles in various ceramic industries.
The physical and optical properties of zircon make it ideal for casting and refractory applications such as sand casting, investment casting as well as mould casting in die-cast processes.
Several nuclear, as well as gas purification industries, use zircon or zirconium chemicals for everyday applications in their industries. Zircons are used as brilliant gemstones. They also provide strength and water resistance to paper and are therefore applied widely in many paper industries. As zircon flours are famous for their absorption power of X-rays emission, thus, they are widely used in television as well as computer screens to absorb X-ray emitting from electron guns in cathode tubes. It can also increase the refractive index and the toughness of the glass.
Zircon Mineral
Zircon minerals are basically silicate minerals that belong to the group of nesosilicates. They are mostly found in sand deposits or metamorphic rocks and are widely spread throughout the solar system. The zirconium mineral makes excellent gemstones when undergoing heat treatments. Most of the zircon minerals or crystals carry radioactive traces and are therefore green in colour. Due to the presence of iron impurities in the zircon mineral, it appears dark brown in colour. The basic structural unit of silicate mineral which is also a basic zircon mineral is silicon tetrahedron. In a silicon tetrahedron, one silica atom is surrounded and is bounded with four oxygen atoms, each placed at the corners of the regular tetrahedron.
Zircon Refractive Index
The refractive index of Zircon is 1.93 -1.98 which is higher than that of its corresponding crystals like topaz, emerald and amethyst. Thus, because of its high refractive index, it makes a brilliant gemstone that has similar refraction to that of a diamond. These gemstones are made when the crystal undergoes heat as well as oxidation treatment. These kinds of treatments for the conversion of raw crystals into gemstones are vastly carried out in Sri Lanka.