Zircon
Zircon is a mineral belonging to the mineral class of " silicates and Germanates ". It crystallizes in the tetragonal crystal system with the chemical composition of ZrSiO4. Zircon has a relatively high Mohs' hardness of 6.5 to 7.5.
The natural color of zircon varies between colorless, yellow gold and red to brown, but can also be green, blue or black to be. The stroke color is white. Specimens that show gem quality because of their size and purity, are a popular substitute for diamonds, with which they are sometimes confused. Zircon is not to be confused with synthetic cubic zirconia ( formula: ZrO2, zirconia ), which also serves as a gemstone and diamond imitation.
Special Features
Zircon often contains impurities and inclusions of various elements and minerals. The theoretical oxide composition of zircon is 67.1 % and 32.9% ZrO2 SiO2. After Rösler (1991 ), it may contain ( U3O8 ) in extreme cases up to 30% hafnium oxide ( HfO2 ), 12% thorium oxide ( ThO2 ) or 1.5 % uranium oxide. Accordingly, the density varies from 4.3 to 4.8 g / cm ³. In particular, the contamination by play hafnium for the preparation of pure zirconium of zirconium to be used in the reactor technology a role because a separation due to the similar characteristics of the two elements is expensive.
Etymology and history
The name derives, gold either from the Arabic zarqun ( ئشقنعى ), vermilion, or from the Persian zargun ( زرگون ). Changes will find these words in the jargon again, so is referred to bright zircons.
Was first described scientifically in 1783 by Abraham Gottlob Werner zircon. The name was first used in 1789 by Martin Heinrich Klaproth for he had discovered " zirconia " and transferred to the gem.
Classification
In the old ( 8th edition ) and new classification of minerals according to Strunz ( 9th Edition ) Zircon belongs to the department of the " island silicates ( nesosilicates ) ".
The revised 9th edition of the Strunz'schen Mineral classification divides this department, however, precisely according to the presence or absence of other anions and the coordination of the cations involved. The zircon is therefore in accordance with the division of the " island silicates without additional anions with cations in oktahedraler and usually greater coordination ", where he, together with coffinite, Hafnon, thorite and thorogummite the unnamed group 9.AD.30.
The commonly used in English-speaking classification of minerals according to Dana assigns the zircon similar to the new Strunz'sche Mineral classification in the department of " island silicates: SiO4 groups with cations in > coordination " where the mineral, also with coffinite, Hafnon forms Thorit and thorogummite an independent group that Zirkongruppe.
Modifications and varieties
- As Hyacinth ( Jacinth ) refers to yellow to brown Zirkonvarietäten.
- Malakon is the name for an opaque, zircon isotropisierten
Education and Locations
Zircon is a formation in front of up to 4.4 billion years ago the oldest known mineral on Earth and the Moon ( see age determination ) and one of the most abundant minerals in the earth's crust. It arises as an early crystallization products primarily in igneous rocks such as granite and alkali-rich rocks such as pegmatites and syenite.
In metamorphic rocks zircon is formed in the form of new or recrystallized grains. In sedimentary rocks can be found detrital zircons, which are transported by erosion and deposited grains. The average size of zircons between 100 and 300 microns, eg in granitoid rocks. Occasionally, however, they reach sizes of several centimeters, especially in pegmatites or heavy mineral soaps.
By analyzing the shape and crystal surface formation of zircons conclusions on the formation conditions and the further development of the zircon can be drawn.
Also, in some mineral samples from the sea floor of the Mid-Atlantic Ridge and the Southwest Indian Ridge and from deep boreholes of the continental shelf off the coast of New Jersey zircon was found. Likewise, in some rock samples of the moon.
Crystal structure
Zircon crystallized tetragonal in the space group I41/amd ( Raumgruppen-Nr. 141) with the lattice parameters a = 6.61 Å and c = 5.98 Å and four formula units per unit cell.
In some zircons of the lattice structure is (uranium, thorium ) partially destroyed by the action of high-energy particles radiogenic - metamiktisiert - such crystals often show darker brown colors. By metamictization water can be incorporated into the crystal lattice. The result is a marked reduction of refractive index, density, and hardness ( see table). Birefringence is not longer present. In this respect, a distinction zircons from their stadiums forth in
- Hochzirkone (normal, crystalline zircons )
- Tiefzirkone ( metamikte zircons )
- Intermediate zircon which are with respect to their properties, between the first two groups.
By heating to about 1000 ° C may be re- Tiefzirkone recrystallized Hochzirkone.
Use
In geology
Since the development of radiometric age determination zircons occur particularly in geochronology meaning: they contain traces of radioactive nuclides 235U, 238U and 232Th ( from 10 ppm to about 5 weight percent). All these isotopes decay via decay chains lead to different isotopes. By measuring the corresponding uranium - lead and thorium -lead ratios the crystallization age of zircon and so often that of the rock containing it can be determined.
Zircons are extremely resistant to weathering and geological factors such as even high-grade metamorphism and can " save " such events in their isotopic composition.
The previously oldest minerals found on earth are zircons from the gneiss Narryer Terran, Yilgarn craton, Western Australia, with an age of 4.404 billion years. The age of the oldest sample of moon rock ( breccia 72215 ) was determined to be 4.417 billion years. Due to the age determination method, the specification corresponds to the crystallization age of the zircons.
As a raw material
Zircon is the most important zirconium and Hafniumerz. It is used for refractory bricks (together with alumina or corundum), as molding sand in foundries, in the glass industry and as an abrasive used. The zirconium dioxide (ZrO2) prepared from zirconium has a melting point of about 2800 ° C and is used for the manufacture of crucibles and abrasion-resistant materials, such as dental implant abutments and crowns / bridge frameworks. Zirconium finds himself among others in nuclear reactors use. The most important reserves are heavy mineral soaps, in which zirconium occurs occasionally in rock-forming individual layers. Zirkonreiche placer deposits are mined in India, USA, Australia, Sri Lanka and South Africa.
Because of its high dispersion of 0.038 (compared with: diamond: 0.044, cubic zirconia: 0.066 and quartz: 0.013) are larger specimens valued precious stones. By heat treatment, the color of brown or turbid zircons can be varied depending on the heat input arising as colorless, blue or golden yellow crystals. In layman's confusion of the colorless zircon diamond is easily possible. So in the 19th century occurring in Sri Lanka colorless zircons were held for inferior diamonds. Similarly, a confusion of the blue zircon spinel is possible for laymen.
Zirkonglas serves the shroud of radioactive waste (eg, plutonium) for final disposal, the container according to current research withstand about 2000 years of radiation. Scientists led by Ian Farnan from the British University of Cambridge, however, have found experimentally that the expected durability of zirconium is against plutonium 239 rather 210 years.
" Zircon " in medicine
In the popular scientific literature zircon is sometimes erroneously referred to as a modern high-performance material in the restoration of medicine, especially in dentistry. However, it does not regularly meant that defined via its chemical formula ZrSiO4 zircon silicate, zirconia ZrO2 but with small admixtures of yttrium oxide to achieve outstanding material properties. The silicate zircon, however, is not used in regenerative medicine.