Gems and jade are mineral raw materials for making various decorations and works of art, and occupy a special position in minerals. The use of gems and jade began in the ancient times when material civilization was formed: as early as the Paleolithic, primitive people decorated themselves or their idols with colored stones. Colored stone products are the records of ancient civilization. Gems, together with gold, have the function of money. Sometimes they are small and valuable. Gems and jade articles still have great economic and cultural significance.
Gem and jade are special minerals. Gem and jade industry use them to make various decorations, souvenirs and handicrafts. Precious (jade) stones include a large number of minerals and mineral aggregates, which all have gorgeous colors, beautiful patterns, crystal clear, dazzling, dichroic and other optical effects, and have high ornamental value. High-quality gems should be solid, that is, quite hard (Mohs hardness rating is above 6) and resistant to ordinary acid and alkali corrosion.
So far, there is no universal name for gem minerals. Some people call the transparent original stone a gem with its own color, while the opaque original stone is called a colored stone. Because most precious stones are natural, these two names are obviously synonyms. Some use "precious original stone". Using the name colored stone is the simplest and most common, although it may not be suitable for some transparent and colorless stones.
Colored stone is a mineral with many characteristics. First, colored stones contain a wide variety of minerals, and their composition and origin are quite inconsistent. At present, there are about 200 kinds of minerals and rocks used in gem and jade industry. With the discovery of stones with high ornamental value (such as hedenbergite, xonotlite-hedenbergite skarn, etc.). ), the number will continue to increase. The value of colored stones depends largely on whether they are widely distributed. No matter how beautiful the colored stones are, if they are widely distributed, they will also depreciate. For example, this happened in Rainbow Labrador. Long ago, it was regarded as a gem, but after some large mineral deposits were discovered in Canada and Ukraine, it became a very common stone. This happened to agate. The reputation of colored stones is also of great significance: some new or unfamiliar colored stones (plagioclase, chrome diopside, kyanite), even if rare, will not be valuable. Recognized gems include diamonds, emeralds, opals, rubies and sapphires, which are collectively called the "Five Gems". Except for precious stones, all the others are ordinary stones. Among more than 2,000 natural minerals that have been identified, less than 100 can be used as gems, of which only 16 is important.
Commercial names are widely used instead of mineral names in colored stone transactions. Generally, it is named after colored gems with similar, familiar and high value, such as tanzanite (Tanzanian blue zoisite), Bohemian ruby and Cape ruby (magnesium aluminum garnet produced in Czechoslovakia and South Africa respectively), Pakistani emerald (Pakistani green calcium aluminum garnet) and so on. Some colored stones also have certain ethnic and religious traditions. For example, in the Near East and Central Asia, people like turquoise and lapis lazuli, in China and Southeast Asia, people like nephrite and jadeite (jadeite), in India, people like ruby and agate, and Orthodox Christians like amethyst.
Due to the complexity and particularity of gemstone production and the uneven distribution of colored stone raw material bases, mining centers and processing centers are often separated in history. Colored gems's mining centers are Zaire, South Africa, Botswana, Madagascar, Brazil, Colombia, India, Sri Lanka, Thailand and Australia. The machining centers are Holland, Israel (mainly grinding diamonds), America, West Germany and Italy.
In order to understand the colorful world of colored stones, people have roughly classified them according to their application fields and relative values. For example, colored stones are divided into two categories: gems and jade, and the one between them, namely gems/jade, is ranked according to its quality (but not rare treasures) and its price in the international market.
Gemstones are generally transparent, and their quality can be reliably identified after processing. The unit of measurement is carat (one carat = 0.2g), and the least valuable gemstone unit of measurement is gram.
The price of precious stones varies greatly. Rare products such as diamonds, rubies and emeralds often become national treasures. They generally have their own proper names, which record their own history and the surprisingly high prices. The price of ordinary high-quality gemstones varies greatly due to different types of gemstones. In the same kind of gem, its price depends on its size.
There are also some inclusions in gem-grade minerals, the most famous of which are star rubies and sapphires with Xing Cai effect (that is, starlight emitted on the cross section perpendicular to the optical axis of the crystal). Xing Cai effect is caused by directional micro-inclusions of acicular rutile. Emerald, that is, inclusions containing a lot of fibrous minerals (usually amphibole), can create a sparkling tiger's eye or cat's eye effect on a golden yellow or green background.
Gem/jade and jadeite are usually single mineral and multi-mineral aggregates with beautiful colors or patterns. This property is obvious on the polished surface, so jadeite raw materials should be polished easily, so there should be relatively uniform fine particles or cryptocrystalline texture. Gems/jade and jade are not like gems, they are opaque or transparent only when sliced.
Gem/jade is the most beautiful, rare and hard stone, the price is close to the fourth-class gem, and some very rare stones can be said to be gems. Some of them are transparent, such as colorless crystals, smoke crystals, amber, etc., but their value is much lower than that of precious stones because of their commonness. The artistic value of gem/jade products is very important. Its quality can be accurately judged according to the original stone, and the unit of measurement is kilogram.
Jade is used to make ordinary sculptures or high-grade building materials. Generally, it can be divided into jadeite (above Mohs hardness table 5), mainly time-based or siliceous mineral aggregates, such as jasper, patterned flint, silicified wood, obsidian, Wen Xiang pegmatite, colored quartzite, burnt quartzite, talc magnesite schist, coarse-grained fluorite and nephrite (below Mohs hardness table 4), such as jade.
In order to make colored stones more beautiful, they are usually processed: splitting, grinding and polishing. Transparent gemstones are first processed in batches (collectively referred to as "batch works" or "work production") to form complex polyhedrons to ensure that light can be fully reflected and refracted. Generally speaking, the main forms of batch work are as follows:
Batch processing of gemstones is a very complicated technological process. We must try our best to keep the maximum weight of the original stone, eliminate or cover up the original defects, and consider the polychromatic nature of the original stone to make the gem glow or thicken in color.
Many colored stones are beautiful, even if they are not processed, or appear in the form of single crystals, clusters and ore blocks. They can be used as excellent specimens.
Gems, especially some kinds of gems and some colors of gems, are of high value, which leads to all kinds of artificially improved natural gems, synthetic gems and new artificial materials, and even all kinds of imitations and fakes. The so-called artificial improvement generally refers to the use of physical methods, such as electron flow, γ -ray irradiation, and heat treatment to change the true color of gems or make them more concentrated. Generally, several physical methods are combined: irradiation can make minerals have the necessary color, and at the same time or subsequent heat treatment can improve the durability of color and make gems shine. At present, the method of improving the color of colored gems by physical means has been widely used, and the improved rough stone is still considered as a natural gem.
There is also a way to change the color, that is, soak the gems with various organic or inorganic substances for dyeing. This method is mainly used to strengthen the color of some opaque stones (turquoise, jadeite, agate, opal, etc.). ) there are micropores.
Some colored stones (such as amber, turquoise, etc. ) after pressure cementation, large blocks can be formed. But its value is far lower than that of nature.
Artificial gem, especially synthetic corundum dyed with chromophores such as chromium, titanium and cobalt, which looks like rubies, sapphires and emeralds, plays a great role in the gem industry at present. Corundum can be easily synthesized with other refractory minerals by melting. For example, spinel is mainly dyed like sapphire, zircon and emerald. Many new decorative materials that are not found in nature, such as garnet, can also be synthesized by melt crystallization. These garnets are transparent, can be dyed into beautiful colors, and have high hardness and large spectral coefficient, which can show color changes.
At high temperature and high pressure, transparent chronotropic crystals dyed in various colors can be cultured in alkaline aqueous solution, including amethyst with iron-alkali color center similar to natural minerals. Corundum and beryl (emeralds) can be obtained by hydrothermal method. Gem opal and turquoise are also synthesized by gilson Laboratory. But so far, artificial decorative diamond has not been produced. Although it can be produced by synthesizing small industrial diamond with ultra-high pressure graphite, it is not economical.
The output of synthetic gemstones is very high. In some places, synthetic gems have actually replaced natural gems. At present, only artificial emeralds and precious opals are expensive.
Imitation is to pass off natural or synthetic gems with similar appearance but low price as real gems. For example, colorless zircon is used to imitate diamonds, spinel and garnet are used to imitate rubies and so on.
There are also many fakes, such as transparent gemstones made of colored glass, amber, turquoise, lapis lazuli and so on made of plastic and resin. There are also semi-fake, glue made to increase the weight of gems: generally, the lower part of real gems is bonded with synthetic products, crystals and even glass, and then embedded in the frame.
The distribution of colored stone raw material resources in the world is extremely uneven. 98% of diamonds are produced in Africa, where there are a large number of emerald deposits and amethyst deposits. Asia has world-famous large ruby and jadeite deposits. Australia is famous for its precious protein, accounting for at least 95% of the world's precious protein production, and there are super-large sapphire deposits there. There are turquoise deposits, tourmaline deposits and nephrite deposits in North America. South America is the main producing area of emerald, beryl, topaz, agate and amethyst.
Colored stone is a special kind of mineral, so the quality requirements of gemstone industry are always relative, not static. This is because the decorative aesthetic attributes of colored stones, especially gems/jade and jade, are often subjective and difficult to specify. For example, foreign mineral inclusions and healed cracks are generally considered as defects of colored stones, but they can also make colored stones more beautiful and prove to be natural. If the ideal transparent gem should be pure in texture and perfect in color, then the rough stone produced by the most famous mineral deposit should be used as a "model" to identify the quality of the gem.
As we all know, a gem should have three elements: beauty, durability and rarity. Some people think that it should have eight elements, namely, beauty, hardness, rarity, transparency, stability, strangeness, harmlessness and weight. For thousands of years, gems have accompanied human beings, which not only beautified and enriched people's lives, but also found that gems have the value of decoration, preservation, currency, medicine, collection and appreciation.
Compared with natural gems, synthetic gems pay more attention to the characteristics of "beauty" and the value of "decoration". In terms of beauty and decoration, synthetic gemstones can be comparable to natural gemstones, and sometimes even exceed natural gemstones.
Because synthetic gemstones are substitutes for natural gemstones, when we synthesize gemstones, we always require synthetic gemstones to be as close as possible to natural gemstones, and the more realistic the better, the highest grade of natural gemstones. Therefore, synthetic gemstones not only have beautiful color, good transparency, high hardness and large crystals, but also have no cracks and rafters, good quality, bright color, purity and flawless texture, which is equivalent to or superior to the corresponding natural gemstones.
It can be seen that the products made of synthetic gemstones as jewelry decoration materials must be as beautiful as those made of similar high-grade natural gemstones. And high-grade natural gemstones are not only rare and hard to find, but even if they are obtained, the price must be surprisingly high; Synthetic gemstones are manufactured and produced in factories or laboratories. Not only can the output be controlled artificially, but the price is also quite cheap. Because of this, it is very natural for people to use synthetic gems as the main material of highly decorative fashion jewelry or imitation jewelry. Besides, these jewelry are beautiful and the price is very low. Most people can afford it, which is well received by the masses and the sales volume is getting higher and higher.
As can be seen from the above, the main value of synthetic gems is decoration, which is beyond reproach.
However, it should be noted that the concept of whether the number of synthetic gems is "rare" is relative. Compared with the high-grade products of similar natural gemstones, synthetic gemstones are not uncommon; However, compared with similar natural gems or materials that can be used for decoration, the number of synthetic gems is still "rare". In addition, many famous synthetic gems, because of their age, will continue to increase in value over time, and some can even reach the level of collection.
The price of synthetic gemstones is quite cheap compared with natural gemstones with the same color and homogeneity. Its cheap range is related to the difficulty of synthesis method and the size of output.
On the whole, its cheap range is between one ten thousandth and one tenth. For example, the price of pigeon blood red ruby ring surface synthesized by hydrothermal method is around 250 yuan per carat. If the natural pigeon blood red ruby is a high-quality product without cotton, crack, inclusion and growth line, its price should be about 25,000 yuan/carat, that is, about one thousandth of the price of pigeon blood red ruby synthesized by hydrothermal method; The price of glass cat's eye imitation natural gold-green cat's eye gem is about one tenth of that.
This is because the hydrothermal synthesis of ruby is difficult, the equipment is expensive and the output is low, so it belongs to synthetic gem. The production process of glass cat's eye imitation natural gold-green cat's eye gem is relatively easy, the equipment is simple, the output is large, it belongs to imitation gem, so the price is cheap. Compared with similar synthetic gems, due to different synthetic methods, the prices are quite different.
For example, the price of ruby synthesized by flame melting method is much lower than that of ruby synthesized by hydrothermal method, because the ruby synthesized by flame melting method is burned by hydrogen and oxygen, and it can grow about 10 gram of ruby per hour. At the same time, each workshop can put a lot of equipment for production, and the output is large. The sales volume of its products is not calculated in carats like rubies grown by hydrothermal method, but in terms of how much per kilogram. At present, the domestic production of flame-fused rubies is generally about 400-650 yuan per kilogram, 1 kg is 1 1,000g, and 1 g is 5 carats, that is, the price of 5000 carats of flame-fused rubies is 400-650 yuan, and the flame-fused rubies per carat is 0. 1 yuan, which is about 2500 times cheaper than the ruby grown by hydrothermal method.
It can be seen that the prices of similar gems grown by different methods are different because of the difficulty of the method and the size of the output. However, it is an objective fact that the price of synthetic gemstones is much cheaper than that of natural gemstones of the same quality.
Gem identification can be divided into three aspects:
(1) The name of the gem, and determine what it is.
(2) material classification, clear material attributes.
③ Gem quality is divided into two poles.
(1) Gemstone naming. For gem identification, the name can be determined by measuring the density and refractive index data of the gem. For example, the measured gem density is 3.52 (0.0 1) g/cm 3, the refractive index is 2.4 17, and the dispersion is O.O44. Combined with its high thermal conductivity, it can be named diamond. If we also have the data of chemical composition and crystal structure of gems, the naming of gems will be more accurate and perfect. On the basis of naming gemstone minerals, they are classified into varieties according to their colors or special light properties (cat's eye, starlight, discoloration and discoloration). For example, beryl gem minerals are divided into green beryl (also known as emerald), blue beryl is called aquamarine, and colorless beryl is called Goshenite. Beryl varieties with special optical properties include beryl cat's eye and starlight beryl. Corundum gem minerals are classified by color. Corundum with special optical properties can be used to paint star ruby, starlight sapphire and sapphire cat's eye.
(2) Material classification. Material classification and identification is one of the most difficult tasks for gem appraisers. Before naming a gem, you must answer the following questions:
Is the gem natural, synthetic or artificial?
② Has the gem been dyed and coated? Oiled or chemically treated?
③ Has the gem undergone heat treatment or color diffusion?
(4) Is the gem irradiated and colored?
⑤ Are the cracks and holes on the gem surface artificially filled?
According to the nature of materials, we divide them into two categories: precious stones and man-made products.
The gem is:
Natural gem: a substance completely formed by nature refers to a natural mineral crystal without artificial influence, which is synonymous with "purity" and "nature". Include various natural materials.
(2) Optimization of gems (artificial treatment of gems): Gems are natural substances, and the quality of gems can be improved by various new methods and means such as chemistry, heat, optics and high-energy ray radiation, so as to enhance their value. Due to the different treatment methods and strengths, it is usually difficult to draw a line between natural gemstones and treated optimized gemstones.
Workpieces are:
(1) Synthetic gemstone: The product crystallized by some artificial method under artificially controlled crystallization conditions, and its physical or chemical properties and crystal structure are basically the same as the corresponding natural gemstone. Such as synthetic diamonds, synthetic rubies and synthetic sapphires.
② Artificial stone: refers to various crystals grown artificially, which have chemical composition, physical properties and crystal structure, and have no natural reference. This artificial stone is an imitation of some precious stones, such as diamond-like artificial cubic alumina (ZrO2 _ 2). Its hardness is higher (8.5), and its optical effect is similar to that of diamond, but its chemical composition, physical properties and crystal structure are different from those of natural diamond, and there is no natural contrast. It can only be called artificial stone, not "synthetic gem".
(3) Assembled stone (also called assembled stone): Assembled stone refers to two or more crystalline or amorphous substances that are combined into products by unnatural methods through adhesives or other means, and its components can be divided into gems, other minerals and chemicals. Split stones entering the market: emerald split stones, ruby split stones, etc.
(4) Imitation: using various materials: chemistry, plastic, glass, artificial crystal, etc. , imitating the effect, appearance or color of natural and synthetic gems, without their chemical properties, physical properties and crystal structure. There are both gemstone imitations and artificial gem imitations.
⑤ Recycled products: The raw materials of precious stones are melted, bonded or fused into an integrated artificial product.
At present, all kinds of artificial products flock to the market one after another, and the task of gem mineralogist is quite heavy to identify all kinds of artificial products to ensure the acquisition of real gems. & gt& gt& gt& gt teaches you four tips for cleaning up apples!
(3) Quality classification of gems. Gemstones are classified into three categories: diamond, colored gems and jade. At present, the principles and methods of grading and the quality grading standards of diamonds are relatively perfect, but the quality grading standards of colored gems and jade have not been universally recognized and unified as 4C standards of diamonds at home and abroad. Diamonds are generally classified by 4C classification standards in the world, namely, weight, color, clarity and cut. China has formulated a national standard for diamond classification, and in principle, it adopts 4C standard. However, it should be noted that people have different tendencies in understanding and mastering 4C standards in different periods, that is, they will pay different attention to 4C. At first, people emphasized the weight and thought that the bigger the diamond, the more valuable it was. Later, it was found that not all big diamonds were of good quality, so they developed to pursue high color grade, the highest clarity, glittering and translucent, and became more precious and rich. What's the next point? People will wait and see! Now it is suggested that the most perfect diamond comes from exquisite cutting. The position of the cutter may rise.
Jewellery circles all over the world are studying to establish a quality grading system for colored gems and jade. It is proposed that the quality grading standards of colored gems and jade should be gradually established and improved on the basis of 4C standard of diamond quality grading, which is a problem that everyone is concerned about at present.