Topaz color

The colors are clear, yellow, orange, red, blue and green, while the main color centers are radiation induced. Violet and violet-red colors in Cr-containing topaz are generated by two absorption bands in the visible part of the spectriun, which are connected with Cr + substituting for AP". Yellow topaz besides Cr +... 

AP+ (0.675 A). Thus from ciystallochemical positions the presence of Mn " in topaz structure is quite possible. Strong absorption bands due to Mn " corresponding to the spin-allowed transitions to levels in the visible to near-UV region generate the yellow color of the phosphors, which corresponds to the yellow color of topaz. Thus we propose that a connection may be considered between the long-lived lines at 697 and 711 nm and Mn + centers, which may be formed as a result of natural irradiation of topaz. 

Color centers in topaz can be produced by irradiation with fast neutrons and gamma-rays (Platonov et al. 1989). It was found that luminescence bands are connected with such color centers, which may be detected by steady state and time-resolved spectroscopy (Marques et al. 2000). The detected luminescence bands have been connected with both impurities and structural changes. 

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. 

Some treatments are practiced so widely that untreated material is essentially unknown in the jewelry trade. The heating of pale Fe-containing chalcedony to produce red-brown camelian is one of these. Another example involves turquoise where the treated material is far superior in color stability. Such treatments have traditionally not been disclosed. Almost all blue sapphire on the market has been heat treated, but it is not possible to distinguish whether it was near-colorless corundum containing Fe and Ti before treatment, or whether it had already been blue and was only treated in an attempt at marginal improvement. The irradiation of colorless topaz to produce a blue color more intense than any occurring naturally is, however, self-evident, and treatments used on diamond are always disclosed. 

The destruction of color centers (1,3) by heating can result in bleaching or fading. Examples are brown or blue topaz, red tourmaline, smoky quartz, and some yellow sapphire. In other instances there may be a color change as when amethyst turns into yellow citrine, or when the heating of a brown topaz reveals the presence of a previously hidden Cr-derived color in a pinked topaz. These changes can usually be reversed by an irradiation treatment. 

With the exception of diamond coloring and the turning of topaz blue, the source of the irradiation is immaterial. Gamma rays are the preferred source because of uniformity of coloration and the absence of heating and induced radioactivity. The most commonly seen gemstones enhanced by irradiation are summarized in Table 4. 

DANBIIRITE. The mineral danburile, CaBjSijO. calcium-boron silicate, crystallizes in the orthorhombic system in prismatic forms somewhat resembling the mineral topaz. Its fracture is subconchoidal brittle hardness, 7 specific gravity. 2.97-3.02 color, colorless, yellowish-white, yellow, dark wine yellow and brownish-yellow luster, vitreous to greasy translucent to transparent. It is found at Danbury. Connecticut, from whence its name was derived. Saint Lawrence County, New York. Switzerland, Japan, and Madagascar. 

Topaz is a rather rare silicate mineral with a Mohs hardness of 8. It comes in many colors from yellow to pink to purple to blue, depending on what ions are present in the crystal. It can even be colorless. However, the favorite variety is orange to brown in color and called imperial topaz. Much of the best topaz comes from Brazil. The gem called London blue topaz can be made from the colorless variety by treatment with heat and radiation. 

The books, for example, with which my study walls were lined. Like the flowers, they glowed, when I looked at them, with brighter colors, a profounder significance. Red books, like rubies emerald books books bound in white jade books of agate of aquamarine, of yellow topaz lapis lazuli books whose color was so intense, so intrinsically meaningful, that they seemed to be on the point of leaving the shelves to thrust themselves more insistently on my attention. ... 

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. 

The next ray represents the topaz and its color is greenish-yellow. There we see plants, reptiles, birds, unknown spectres, roses, and dark people. This is one more grade of this knowledge. 

Topaz or sapphire irradiated to a yellow or brown color No No, only fact of fading Explained... 

Tourmaline, spinel, and topaz occur in many colors. Pink and green varieties of tourmaline are the most popular, and the red varieties of spinels are the most valued. Good specimens of pink topaz are the most expensive. 

The required fluence is dependent on the specific batch of topaz stones and the depth of the desired blue coloration. The fast neutron fluence is typically of the order of 10 -10 n cm. For a 2 MW research reactor, about 50 to 100 hours of irradiation is required to achieve this fluence. 

If the temperature of the gemstones approaches 300°C the damage to the topaz will anneal and de-coloration will occur. In addition, if the temperature is too high the stones will be prone to flaking during post-irradiation handling. A typical temperature during irradiation should be... 

Topaz AljFjSiO, An orthorhombic mineral The color is white or lightly... 

Figure M54) that occurs as prismatic crystals and as rounded water-worn pebbles colored. A transparent topaz is used as a gemstone... 

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