Since ancient times, rubies have been regarded as treasures. In European mythology, the birthstone in July is ruby, which is a symbol of love. At the wedding of the European royal family, ruby ​​is often used as a witness to marriage. There are countless romantic legends related to rubies, and the Bible also considers rubies and wisdom to be related to beauty. So why does ruby ​​become the pursuit and yearning for so many people? Today we will unveil the mysterious veil of ruby ​​together~
Ruby refers to the red corundum, the color of the best ruby ​​is "pigeon blood red". The crystal form of corundum is Al2O3, and the pure corundum is colorless. Natural corundum crystals often contain a small amount of Cr, Fe, Mn, Ti, Ni, Co, V and other elements to replace Al in a similar way, so that the crystal presents a variety of colors. The corundum containing Cr is red, ie ruby; the corundum containing Fe and Ti will appear blue, the yellow containing Ni will appear yellow, and the color containing Co and V will appear green. In addition to the red corundum, the corundum of all the colors are sapphire, and the front can be decorated with colors such as pink sapphire, yellow sapphire, green sapphire and so on. Some jewelers also classify pink corundum as a ruby ​​sequence, which is not strictly rigorous in mineralogy classification.
Corundum is the second hard mineral in nature with a hardness of 9, which is second only to diamond (10 hardness), also known as diamond. Due to its high hardness and low price relative to diamond, corundum is often used as a substitute for diamonds for sandpaper or abrasive materials. Corundum is a glass luster to a ruthenium gloss with a high reflectance. The corundum minerals are trigonal, the crystals are mostly barrel-shaped and columnar, and a few are plate-like parallel to the (001) plane. The corundum crystal is unjointed, but the crack is developed. Ruby is a kind of corundum, and it is difficult to be spared. Therefore, there is often a saying that "ten red and nine cracks". When there is a fine inclusion in the mineral crystal (see below), or when an external force is received, cracking occurs along the weak surface of the crystal mechanics, that is, cracking. Cracking is not an intrinsic property of minerals, nor does it strictly follow the crystal lattice structure.
Natural rubies in nature often contain all kinds of inclusions, which affects the value of rubies as gemstones to a certain extent. Rare and transparent natural rubies are extremely rare. When the ruby ​​contains a large number of fine needle-shaped rutile inclusions, and the rutile is distributed on the 0001 surface along the intersection of the crystal planes and intersects each other at 120°, the ruby ​​is processed along the c-axis of the crystal into a curved surface, and starlight can appear. The effect is usually six-shot starlight, and a small amount is twelve-shot starlight. The starlight effect is unique to the trigonal gem-quality minerals.
Ruby improvement
Most of the natural rubies cannot be directly used as raw materials for gemstones due to the influence of color, transparency, cracking, inclusions, etc., and require certain processing improvements.
The hot working method is the most common way of ruby ​​treatment. The ruby ​​is heated to a temperature of 1000 ° C for a suitable time to remove the purple or blue hue in the ruby. The hot processing is purely physical and does not change the chemical composition of the ruby. The heat treated ruby ​​can still be considered a pure natural ruby. Heat treatment is also an approved method of ruby ​​approved by the International Jewelry Association.
In order to compensate for the cracks in the ruby ​​or to wrap the air bubbles inside and increase the transparency, a filling treatment method, that is, filling with leaded glass, borax or organic glue, and superimposing heat treatment to heal the defects of the ruby ​​may be employed. The chemical composition of the filled ruby ​​changes.
Another deceptive treatment is diffusion treatment, which introduces external pigments into the surface of the gemstone, increasing the vividness of the ruby ​​color, or creating a star-light effect floating on the surface.
Identification of rubies
Ruby is very popular because of its special color and superior performance, it has high ornamental value and economic value. But with the massive development of high-quality ruby ​​mineral resources, natural high-quality rubies are becoming scarcer. This on the one hand leads to the increasing popularity of ruby, and on the other hand, some merchants use red zircon, spinel, tourmaline, garnet, etc. to pretend to be ruby. In industrial rubies, artificial synthesis has also become an alternative production method for natural rubies. This brings some problems to the ruby ​​identification.
Ultraviolet radiation is an effective means of identification, and tools are readily available, and UV detectors are generally UV-based. Ruby is fluorescent and produces weak red fluorescence under both long-wave and short-wave ultraviolet radiation. Zircon and garnet generally do not fluoresce under ultraviolet light. The red tourmaline is light pink under ultraviolet light. The color of the spinel under ultraviolet light is similar to Chinese red.
Laser Raman is another efficient, non-destructive, and accurate method of identification that not only identifies the true and false rubies, but also identifies whether rubies are natural or artificial, and whether rubies are heat treated and filled.
The Raman spectral characteristics of the corundum minerals are similar, and their peaks are 378, 417, 430, 447, 576, 645, 750 cm-1, respectively. The different mineral Raman peaks are different in intensity. The same mineral laser has different incident angles and characteristic peaks. Will change. For ruby, when the incident light is parallel to the c-axis, 645 cm-1 is the strongest peak except 417 cm-1. When the incident light is perpendicular to the c-axis, the 645 cm-1 peak disappears and is replaced by 576 and 750 cm-1. The incident angle of the laser is different, and the characteristic peak of the Raman changes, which is caused by the anisotropy of the ruby ​​crystal.
Synthetic rubies often exhibit a strong and symmetrical background of fluorescence in the Raman spectrum, which is not found in natural rubies. In addition, synthetic rubies will exhibit a characteristic peak of 785 cm-1, which is related to the presence of transition or rare earth elements and does not occur in natural rubies. In the synthesis of rubies, oxides of Mo, Bi, and W are often added to the raw materials as fluxes, and these elements become integral parts of synthetic ruby ​​crystals. In addition, synthetic rubies can be distinguished by bending growth streaks, elongated bubbles, unmelted raw material particles, and the like.
In addition to the above characteristic peaks, in the 800-2000 cm-1 region, ruby ​​has a small and broad characteristic peak at 1353 cm-1. If the ruby ​​is filled with vitreous, a characteristic peak appears at 1356 cm-1. If the ruby ​​is filled with an organic gum, a characteristic peak appears in the range of 2300-3500 cm-1. The laser-Raman method of hot-processed ruby ​​is identified with certain contingency. A characteristic peak of 710 and 1085 cm-1 appears in the ruby, indicating that the ruby ​​contains a calcite inclusion, and the ruby ​​is not heat treated. Since the melting point of calcite is 825 ° C and the temperature of ruby ​​heat treatment is 1000 ° C, the calcined inclusions in the heat treated rubrite melt and do not exist in the form of crystals. However, this method of identification has limitations because it can only be judged that the ruby ​​containing the calcite inclusions has not been heat treated, and it cannot be judged that the calcite-free inclusions have been subjected to heat treatment.
Therefore, when you buy rubies, please pay attention to distinguishing the merchant's exaggeration of the gems sold. If an individual lacks the expertise and professional equipment to be identified, the most reliable way is to ask for an identification certificate. The authoritative source of ruby ​​in the world is the Swedish GRS certificate. The most authoritative in China is the national inspection certificate, the NFTC certificate. The two certificate standards and descriptions are slightly different, but they can all be officially certified as ruby ​​grades.
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