Zircon color

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

Zirconium oxide is used in the production of ceramic colors or stains for ceramic tile and sanitary wares. Zirconia and siHca are fired together to form zircon in the presence of small amounts of other elements which are trapped in the zircon lattice to form colors such as tin—vanadium yellow, praseodymium—zircon yellow [68187-15-5] vanadium—zircon blue [12067-91 -3] iron—zircon pink [68412-79-3] indium—vanadium orange (105—108). 

Another desirable property for a ceramic color is a high refractive index. For example, valuable pigments are based on spinels [1302-67-6] ( 2jj = 1.8) and on zircon ( 2j = 1.9), but no valuable pigments are based on apatite ( 2j = 1.6), even though the lattice of apatite is as versatile for making ionic substitutions as that of spinel. 

T Name from zargun (Arabic = gold color), a reference to the semiprecious stone zircon. 

Blue water gas, 6 784-790, 827 Blue-white, and blackbody color, 7 327 Blue zircon pigment, 19 404 Blumlein configuration, 14 690 B-matrix, 3 587-588... 

To discrete inclusions, sometimes easily recognizable as zircons, (Figure 6a, b) or complex inclusions made up of strongly colored particles (Figure 6c, d). These inclusions have variable radioactivities. (Figure 6e, f). 

Other Synthetic Materials. Many other natural gemstone materials have been duplicated in the laboratory on an experimental basis, often only in small sizes. Examples include tourmaline [1317-93-7], topaz [1302-59-6], and zircon [1490-68-2]. Of some potential is synthetic jadeite [12003-54-2], one of the two forms of jade. This crystallizes under medium pressure in polycrystalline form from an NaAlS Og glass (qv) and can be colored green by Fe or lavender by Mn (16). Many gemstone-like materials have been grown for technological purposes and such material is sometimes faceted. 

ZrSi04. Based on the mechanism of color formation, zircon pigments can be divided into two categories, substitution-defect pigments and inclusion pigments. 

Gem quality crystals from Ceylon (Sri Lanka) have been known for many years. They range from colorless to brownish orange, yellow, dark red, from light reddish-violet. Heat treated zircons provide a beautiful stone of light blue color. Colorless stones are used as a diamond substitute. 

Zircon is native zirconium silicate (ZrSi04) that exhibits beautiful transparent crystals and a Mohs hardness of 7.5. The tetragonal crystals are usually brownish yellow in color. Also known as jargon or jargoon, zircon is a stable and durable silicate crystal. Small crystals of zircon are among the oldest mineral grains ever found on Earth. 

Diamonds are the hardest natural substance, but they can cleave easily. They occur in every color, but shades of yellow and brown are most common. Today s faceted diamonds are cut and polished with tools embedded with tiny diamond chips or dust. Before the advent of modern methods, diamonds were used in their natural state, or roughly shaped and polished by hand. The hardness of this mineral led many early jewelers to do a minimum of work before setting diamonds in jewelry or regalia. Common imitations of diamond are colorless spinel, sapphire, zircon, topaz, quartz, and many synthetics. 

Colorless zircon has been used as an imitation of diamond, since it has a very high refractive index. Zircon gems are doubly refractive, which can give them a cloudy appearance. Looking through the top of a faceted zircon, the back facet edges will appear double. Zircons come in many colors, and this gem is often heat-treated to change or enhance the color. 

Complex inorganic colored pigments are solid solutions or compounds consisting of two or more metal oxides. One oxide serves as a host and the other oxide(s) inter-diffuse into the host crystal lattice. This interdiffusing is accomplished at temperatures generally in excess of 1000°C. Of the 14 possible crystal structures, the two most important for plastics applications are rutile and spinel. A third structure, zircon, will be briefly mentioned. 

Fig. 9. The core shell pigment zircon red (top) consists of 90-95% shell (Si02-Zr02) and 5-10% core (color). The cobalt blue pigment (middle) and the black pigment (bottom) are much smaller. (Note the different magnification.)...

Zirconium occurs in nature principally as the mineral zircon, ZrSi04. Zircon crystals are found in a variety of colors—white, blue, green, and red—and because of its beauty and hardness (7.5) the mineral is used as a semi-precious stone. The principal oxidation state of zirconium is 4-4 the states - -2 and - -3 are repre> sented by only a few compounds. 

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