12 Photos
Zircon
Chemical Formula	ZrSiO4
Species	Silicates
Crystal System	Tetragonal
Mohs Scale	7
Specific Gravity	4.6-4.7
Color	Reddish brown, yellow, green, blue, gray, colorless; in thin section, colorless to pale brown
Streak	White
Luster	Adamantine, Vitreous, Greasy
Refractive Index	n = 1.925 - 1.961 n = 1.980 - 2.015
Diaphaneity	Transparent, Translucent, Opaque
Cleavage	Poor/IndistinctIndistinct on
Fracture	Conchoidal
Crystal Habit：tabular to prismatic crystals, irregular grains, massive
Geological Setting：An accessory mineral in igneous and metamorphic rocks.

Zircon (/?z?rk?n/; including hyacinth or yellow zircon) is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO₄. A common empirical formula showing some of the range of substitution in zircon is (Zr_1–y, REE_y)(SiO₄)_1–x(OH)_4x–y. Zircon forms in silicate melts with concentrated incompatible elements and accepts high field strength elements into its structure. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green. Colorless specimens that show gem quality are a popular substitute for diamond; these specimens are also known as "Matura diamond".

The name derives either from the Syriac word ??????? zargono, from the Arabic word zarqun (?????), meaning vermilion, or from the Persian zargun (?????), meaning golden-colored. These words are corrupted into "jargoon", a term applied to light-colored zircons. The English word "Zircon" is derived from "Zirkon," which is the German adaptation of these words. Yellow zircon is called "hyacinth", from the flower hyacinthus, whose name is of Ancient Greek origin; in the Middle Ages all yellow stones of East Indian origin were called hyacinth, but today this term is restricted to the yellow zircons.

Thorite (ThSiO₄) is an isostructural related mineral.

Properties

Zircon is ubiquitous in the crust of Earth. It occurs in igneous rocks (as primary crystallization products), in metamorphic rocks and in sedimentary rocks (as detrital grains). Large zircon crystals are rare. Their average size in granite rocks is about 0.1–0.3 mm, but they can also grow to sizes of several centimeters, especially in pegmatites.

Because of their uranium and thorium content, some zircons might undergo metamictization. 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.

Zircon occurs in many colors, including red, pink, brown, yellow, hazel, or black. It can also be colorless. The color of zircons can sometimes be changed by heat treatment. Depending on the amount of heat applied, colorless, blue, or golden-yellow zircons can be made. 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 produce color centers. Color in this red or pink series is annealed in geological conditions above the temperature about 350 °C.

Applications

Zircon is mainly consumed as an opacifier in the decorative ceramics industry. It is also the principal precursor not only to metallic zirconium, although this application is small, but also to all compounds of zirconium including zirconium oxide (ZrO₂), one of the most refractory materials known.

Occurrence

Zircon is a common accessory to trace mineral constituent of most granite and felsic igneous rocks. Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands. Zircon is rare within mafic rocks and very rare within ultramafic rocks aside from a group of ultrapotassic intrusive rocks such as kimberlites, carbonatites, and lamprophyre, where zircon can occasionally be found as a trace mineral owing to the unusual magma genesis of these rocks.

Zircon forms economic concentrations within heavy mineral sands ore deposits, within certain pegmatites, and within some rare alkaline volcanic rocks, for example the Toongi Trachyte, Dubbo, New South Wales Australia in association with the zirconium-hafnium minerals eudialyte 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.^{[citation needed]}

Radiometric dating

Zircon has played an important role during the evolution of radiometric dating. Zircons contain trace amounts of uranium and thorium (from 10 ppm up to 1 wt%) and can be dated using several modern analytical techniques. Because zircons can survive geologic processes like erosion, transport, even high-grade metamorphism, they contain a rich and varied record of geological processes. Currently, zircons are typically dated by uranium-lead (U-Pb), fission-track, and U+Th/He techniques.

Zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, have yielded U-Pb ages up to 4.404 billion years, interpreted to be the age of crystallization, making them the oldest minerals so far dated on Earth. In addition, the oxygen isotopic compositions of some of these zircons have been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. This interpretation is supported by additional trace element data, but is also the subject of debate.

Gallery

Similar minerals

Hafnon (HfSiO₄), xenotime (YPO₄), béhierite, schiavinatoite ((Ta,Nb)BO₄), thorite, (ThSiO₄), and coffinite (USiO₄) all share the same crystal structure (^VIIIX ^IVY O₄) as zircon.