The name derives from thePersianzargun, meaning "gold-hued".[11] This word is changed into "jargoon", a term applied to light-colored zircons. The English word "zircon" is derived fromZirkon, which is the German adaptation of this word.[12] Yellow, orange, and red zircon is also known as "hyacinth",[13] from the flowerhyacinthus, whose name is ofAncient Greek origin.
Optical microscope photograph; the length of the crystal is about 250μm
Zircon is common in thecrust of Earth. It occurs as a commonaccessory mineral inigneous rocks (as primary crystallization products), inmetamorphic rocks and as detrital grains insedimentary rocks.[2] Large zircon crystals are rare. Their average size ingranite rocks is about 0.1–0.3 mm (0.0039–0.0118 in), but they can also grow to sizes of several cm, especially inmaficpegmatites andcarbonatites.[2] Zircon is fairly hard (with a Mohs hardness of 7.5) and chemically stable, and so is highly resistant to weathering. It also is resistant to heat, so that detrital zircon grains are sometimes preserved in igneous rocks formed from melted sediments.[14] Its resistance to weathering, together with its relatively high specific gravity (4.68), make it an important component of the heavy mineral fraction of sandstones.[5]
Because of theiruranium[15] andthorium content, some zircons undergometamictization. Connected to internal radiation damage, these processes partially disrupt the crystal structure and partly explain the highly variable properties of zircon. As zircon becomes more and more modified by internal radiation damage, the density decreases, the crystal structure is compromised, and the color changes.[16]
Zircon occurs in many colors, including reddish brown, yellow, green, blue, gray, and colorless.[2] The color of zircons can sometimes be changed by heat treatment. Common brown zircons can be transformed into colorless and blue zircons by heating to 800 to 1,000 °C (1,470 to 1,830 °F).[17] In geological settings, the development of pink, red, and purple zircon occurs after hundreds of millions of years, if the crystal has sufficient trace elements to producecolor centers. Color in this red or pink series is annealed in geological conditions above temperatures of around 400 °C (752 °F).[18]
Structurally, zircon consists of parallel chains of alternating silica tetrahedra (silicon ions in fourfold coordination with oxygen ions) and zirconium ions, with the large zirconium ions in eightfold coordination with oxygen ions.[19]
Zircon is mainly consumed as anopacifier, and has been known to be used in the decorative ceramics industry.[20] It is also the principal precursor not only to metalliczirconium, although this application is small, but also to all compounds of zirconium includingzirconium dioxide (ZrO2), an importantrefractory oxide with a melting point of 2,717 °C (4,923 °F).[21]
Other applications include use in refractories and foundry casting and a growing array of specialty applications aszirconia and zirconium chemicals, including in nuclear fuel rods, catalytic fuel converters and in water and air purification systems.[22]
Ford Motor Company used a sand casting method known as theCosworth Casting Method for the cylinder heads of itsDuratec V6 engine. The process, developed by noted scientistJohn Campbell used zircon as its casting aggregate to improve material uniformity and create dimensional accuracy, high strength, and a dense, low- or no-porosity structure.[23][24]
A pale blue zircon gemstone weighing 3.36 caratsThis bracelet has zircon gemstones. The metal is zinc alloy base with silver coating.
Transparent zircon is a well-known form of semi-preciousgemstone, favored for its highspecific gravity (between 4.2 and 4.86) and adamantineluster. Because of its highrefractive index (1.92) it has sometimes been used as a substitute fordiamond, though it does not display quite the sameplay of color as a diamond. Zircon is one of the heaviest types of gemstone.[27] ItsMohs hardness is between that of quartz and topaz, at 7.5 on the 10 point scale, though below that of the similar manmade stonecubic zirconia (8-8.5). Zircons may sometimes lose their inherent color after long exposure to bright sunlight, which is unusual in a gemstone. It is immune to acid attack except bysulfuric acid and then only when ground into a fine powder.[28]
Most gem-grade zircons show a high degree ofbirefringence which, on stones cut with a table and pavilion cuts (i.e., nearly all cut stones), can be seen as the apparent doubling-up of the latter when viewed through the former, and this characteristic can be used to distinguish them from diamonds and cubic zirconias (CZ) as well as soda-lime glass, none of which show this characteristic. However, some zircons from Sri Lanka display only weak or no birefringence at all, and some other Sri Lanka stones may show clear birefringence in one place and little or none in another part of the same cut stone.[29] Other gemstones also display birefringence, so while the presence of this characteristic may help distinguish a given zircon from a diamond or a CZ, it will not help distinguish it from, for example, atopaz gemstone. The high specific gravity of zircon, however, can usually separate it from any other gem and is simple to test.
Also, birefringence depends on the cut of the stone in relation to itsoptical axis. If a zircon is cut with this axis perpendicular to its table, birefringence may be reduced to undetectable levels unless viewed with a jeweler'sloupe or other magnifying optics. The highest grade zircons are cut to minimize birefringence.[30]
The value of a zircon gem depends largely on its color, clarity, and size. Prior to World War II, blue zircons (the most valuable color) were available from many gemstone suppliers in sizes between 15 and 25 carats; since then, stones even as large as 10 carats have become very scarce, especially in the most desirable color varieties.[30]
Synthetic zircons have been created in laboratories.[31] They are occasionally used in jewellery such as earrings. Zircons are sometimes imitated byspinel and syntheticsapphire, but are not difficult to distinguish from them with simple tools.
Zircon fromRatanakiri province in Cambodia is heat treated to produce blue zircon gemstones, sometimes referred to by the trade namecambolite.[32]
World production trend of zirconium mineral concentrates
Zircon is a common accessory to trace mineral constituent of all kinds of igneous rocks, but particularlygranite andfelsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands.[33][34] Zircon can occasionally be found as a trace mineral inultrapotassic igneous rocks such askimberlites, carbonatites, and lamprophyre, owing to the unusual magma genesis of these rocks.[35][36]
Zircon forms economic concentrations withinheavy mineral sands ore deposits, within certainpegmatites, and within some rare alkaline volcanic rocks (for example the Toongi Trachyte inDubbo, Australia)[37] in association with the zirconium-hafnium mineralseudialyte and armstrongite.
Australia leads the world in zircon mining, producing 37% of the world total and accounting for 40% of world EDR (economic demonstrated resources) for the mineral.[38] South Africa is Africa's main producer, with 30% of world production, second after Australia.[39]
SEM-CL image of Zircon grain showing zonations and poly-cycles (core-rim structure)
Zircon has played an important role during the evolution ofradiometric dating. Zircons contain trace amounts ofuranium andthorium (from 10ppm up to 1 wt%)[15] and can be dated using several modern analytical techniques. Because zircons can survive geologic processes likeerosion, transport, and even high-grademetamorphism, they contain a rich and varied record of geological processes. Currently, zircons are typically dated byuranium–lead (U–Pb),fission-track, and U+Th/He techniques. Imaging the cathodoluminescence emission from fast electrons can be used as a prescreening tool for high-resolutionsecondary-ion mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest for isotope analysis. This is done using an integrated cathodoluminescence and scanning electron microscope.[40]Zircons in sedimentary rock can identify the sediment source.[41]
Zircons fromJack Hills in theNarryer Gneiss terrane,Yilgarn craton,Western Australia, have yieldedU–Pb ages up to 4.404 billion years,[42] interpreted to be the age of crystallization, making them theoldest minerals so far dated on Earth. In addition, theoxygenisotopic compositions of some of these zircons have been interpreted to indicate that more than 4.3 billion years ago there was already liquid water on the surface of the Earth.[42][43][44][45] This interpretation is supported by additional trace element data,[46][47] but is also the subject of debate.[48][49][50] In 2015, "remains ofbiotic life" were found in 4.1-billion-year-old rocks in the Jack Hills of Western Australia.[51][52] According to one of the researchers, "Iflife arose relatively quickly onEarth ... then it could be common in theuniverse."[51]
^Van Westrenen, Wim; Frank, Mark R.; Hanchar, John M.; Fei, Yingwei; Finch, Robert J.; Zha, Chang-Sheng (January 2004). "In situ determination of the compressibility of synthetic pure zircon (ZrSiO4) and the onset of the zircon-reidite phase transition".American Mineralogist.89 (1):197–203.Bibcode:2004AmMin..89..197V.doi:10.2138/am-2004-0123.S2CID102001496.
^abWilde, Simon A.; Valley, John W.; Peck, William H.; Graham, Colin M. (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago".Nature.409 (6817):175–178.Bibcode:2001Natur.409..175W.doi:10.1038/35051550.PMID11196637.S2CID4319774.
^Valley, JW; Lackey, JS; Cavosie, AJ (2005). "4.4 billion years of crustal maturation: Oxygen isotopes in magmatic zircon".Contributions to Mineralogy and Petrology.150:561–580.doi:10.1007/s00410-005-0025-8.S2CID53118854.
^Ushikubo, Takayuki; Kita, Noriko T.; Cavosie, Aaron J.; Wilde, Simon A.; Rudnick, Roberta L.; Valley, John W. (2008). "Lithium in Jack Hills zircons: Evidence for extensive weathering of Earth's earliest crust".Earth and Planetary Science Letters.272 (3–4):666–676.Bibcode:2008E&PSL.272..666U.doi:10.1016/j.epsl.2008.05.032.
^Nemchin, A.; Pidgeon, R.; Whitehouse, M. (2006). "Re-evaluation of the origin and evolution of >4.2 Ga zircons from the Jack Hills metasedimentary rocks".Earth and Planetary Science Letters.244 (1–2):218–233.Bibcode:2006E&PSL.244..218N.doi:10.1016/j.epsl.2006.01.054.
^Cavosie, A.J.; Valley, J.W.; Wilde, S.A. (2005). "Magmatic δ18O in 4400–3900 Ma detrital zircons: A record of the alteration and recycling of crust in the Early Archean".Earth and Planetary Science Letters.235 (3–4):663–681.Bibcode:2005E&PSL.235..663C.doi:10.1016/j.epsl.2005.04.028.
^Valley, JW; Cavosie, AJ; Ushikobo, T; Reinhardt; Lawrence, DF; Larson, DJ; Clifton, PH; Kelly, TF; Wilde, SA; Moser, DE; Spicuzza, MJ (2014). "Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography".Nature Geoscience.7 (3):219–223.Bibcode:2014NatGe...7..219V.doi:10.1038/ngeo2075.
Hermann Köhler (1970). "Die Änderung der Zirkonmorphologie mit dem Differentiationsgrad eines Granits".Neues Jahrbuch für Mineralogie - Monatshefte.9:405–420.
