GemologyWritten by Alain Darbellay GGGems
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other things of methylene iodide which shows an index of refraction of 1.81 (this liquid is toxic) Dichroscope of which principal part is made up of a tube comprising a window with one of ends and a lens with other, between two is assembled a piece of calcite, chosen because of its strong double refraction so that two images of window appear side by side to observer which looks in eye-glass. The light of adjacent images of window vibrates in two perpendicular plans one to other at a rate of one only plan for each image. The rotation of stone is a significant factor during control of dichroism, bus in all double refraction stones, it exists one or two directions of unirefringence, known as optical axe. The Chelsea color filter. There is a very effective means to reveal subjacent differences in color, it is use of colored filters. They are especially effective in differentiation of natural and synthetic emerald. The optical fiber lamp is useful to distinguish inclusions in rough stones. Microscopes: binocular one, i.e. to double objective is best adapted for gemology. The microscope is of first importance in detection of counterfeits. Indeed, study of inclusions which stone can contain is a practical means to identify gems while explaining to a certain extent conditions under which they were formed in nature. The spectroscope concerns an extremely simple method which allow identification of all stones; rough or polished not being able to be seen with refractometer and which even makes it possible to distinguish certain synthetic or glasses. This method makes it possible to analyze nature of dye of stone. The way in which spectroscope analyzes various wavelengths of light is in theory very simple; that depends on different degree of refraction to which its subjected various rays of each color (wavelength) when they are propagated through a prism of glass or another transparent substance. After having passed through a prism, a narrow parallel beam of white light is spread out in a ribbon with colors of rainbow, visible spectrum. Let us note that a powerful instrument used in many fields of science is at disposal of gemologists, it is microscope of Raman which spectroscopy supplements traditional technology of laboratory. This instrument can give information on samples lower than 1µm what is not accessible to any technique. The use of Raman spectroscopy by imagery is single in order to determine in a nondestructive way molecular composition of inclusions present in gems. Analyze by fluorescence: four kinds of radiation are used. The first consists simply in passing a powerful luminous ray of a lamp of projection of 500W through a balloon filled with a strong copper sulfate solution, this last absorbs all red light, orange and yellow and filter rays are invisible if one observes through a good red or orange filter. If a substance only lit by beam of blue light in which it is shines while being observed through one of these filters, it emits a fluorescence. The second method of stimulation of fluorescence is used, it uses a lamp with high pressure out of quartz, and whose light is filtered through glass of Wood. The third uses ultraviolet radiations of short radiation emitted by a quartz-mercury lamp with low pressure, in which mercury line with 2537 Å is dominating. X-rays represent fourth source of radiation, they are dangerous unless source is not seriously armored. The unit weight and its measurement. It frequently occurs that only an approximate value of density of a stone is necessary to differentiate between gems from similar appearance; in this case a control from density can be carried out by means of liquors of density. The principle of method is simple. A stone will be inserted in a less dense liquid, will float in a denser fluid and will remains in suspension in a liquid of equal density. The three liquids are: The bromoforme density 2,9. The methylene iodide density 3,33. The liquor of Clerici density 4,15. PRINCIPAL COLORING ELEMENTS IN THE GEMS. Chromium Ruby, Emerald, Pyrope garnet, grossularite and uvarovite, Tourmaline. Copper Dioptase, Malachite, Azurite. Iron Sapphire, Aquamarine, Citrine, Almandin garnet. Manganese Morganite, Pink tourmaline, Spessartite garnet. Nickel Chrysoprase. Titanium Blue Sapphire. Vanadium Green beryl, Blue zoïsite , Garnet. GGGEMS.COM © 1987 - 2004 gggems.com All rights reserved. Cutting Styles ¦ Fancy Cutting ¦ Characteristics ¦ Crystalline Systems ¦ Size & Weight
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| | Ilakaka Madagascar ( Sapphire rush )Written by Alain Darbellay GGGems
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· VOHIMENA VAOVAO, 25 kilometers far from Ilakaka. One of quote headlight of sapphires production. The higher edges of rivers abound in sapphires, chrysoberyls, etc. Here in area of Vohimena vaovao. The sandstones, fragile, have been knife cut by river. SANDSTONES of ISALO The base of group of Isalo is entirely continental. Sometimes significant marine incursions and of long duration were introduced into medium and higher parts. The group of Isalo begins at top from lower Triassic and continues until end of Jurassic means. One separates there: Isalo I, at base, especially sandy, continental. Isalo II, argilo - sandy with some marine intercalations. Isalo III, argilo - sandy with side passage to great marine formations. The essential characteristic of Isalo formations is their main constitution of soft sandstones, very permeable, badly cemented which disaggregate easily on surfaces by giving thick siliceous sand coverings. The porous nature of sandstones constitutes an excellent tank which stores water of rains to restore it during dry season. · Sakalama, 60 kilometers south from Ilakaka. MADAGASCAN CORUNDUMS At back, ruiniform sandstones of Isalo range. GGGEMS.COM © 1987 - 2004 gggems.com All rights reserved. ¦ Madagascar Safari ¦ Madagascar Safari 2 ¦ Pakistan Gem Safari ¦ Sakalama ¦
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