(A) diamonds-the king of gems (Figure 8-2)
Figure 8-2 Blue Diamond (Rui Liu et al., 2007)
The scientific name of mineral is diamond, and it becomes diamond after pondering. Mohs hardness is 10, which is the hardest substance in the world at present, and its polished surface is always as bright as a mirror. The refractive index is as high as 2.4, and the refractive index of most gems is below 1.8. Strong dispersion, flickering when the light shines, extremely charming, and has a strong "fire". The color is colorless, but the dark and transparent ones are all treasures, and the light blue ones are the best. The chemical properties are very stable. Defects are too brittle, easy to break, and can not withstand high temperatures above 800℃. The output is small, only about 20% of diamond minerals can be processed into diamonds, and the rest can only be used for industrial purposes. Diamonds produced in nature are mostly octahedron, dodecahedron, diamond, cube and so on. On the crystal surface, there are often inverted triangular pits. People have used diamonds for more than 2,000 years, but the particles are very small. There are less than 2,000 particles with a mass greater than 100 carat, less than 500 particles with a mass greater than 200 carat, and only 20 particles with a mass greater than 500 carat, which is extremely rare. Cullinan, the largest diamond in the world, was discovered in 1905, with a mass of 3. 106 carats, which is equivalent to the fist size of an adult man.
Diamonds smaller than 0.24 carats are small diamonds, those between 0.25 and 0.99 carats are medium diamonds, and those above 1 carat are large diamonds. People divide 1 carat into 100 parts, and each part is 1 cent.
Diamond rough stone: because of its extremely high hardness, it can be identified by scoring or thermal conductivity meter;
Diamond products (visible to the naked eye): have a strong affinity for oil. When you touch a surface with your hand, it will immediately stick with a layer of grease. If you drop a small drop of water on the surface, it will form a ball. If it is scattered, it will be fake diamonds.
There is a kind of "artificial zircon" specially used to counterfeit diamonds, which is very close to diamonds in nature and can be identified by thermal conductivity meter or according to its relative density, because the relative density of zircon is very high.
At present, 27 countries in the world produce diamonds. Diamonds were first discovered in India, and diamonds in South Africa are famous for their large size. More than 65,438+0,900 diamonds have been found in the world, 95% of which are produced in South Africa. Australia is the largest diamond producer with an annual output of 7,000 tons. In addition, there are Brazil, Zaire, Russia and other countries.
Diamonds from China are mainly produced in Yuanjiang, Hunan, Wafangdian, Liaoning, Linshu and Mengyin, Shandong.
(2) Sister gems-Ruby (Figure 8-3) and Sapphire (Figure 8-4)
Figure 8-3 Ruby Original Stone (Rui Liu et al., 2007)
Figure 8-4 Starlight Sapphire (Rui Liu et al., 2007)
1. feature
Both of them belong to corundum, with chemical component Al2O3, hexagonal barrel or columnar crystal shape, hardness 9, brittleness, collision resistance, incombustible below 2050℃ and insoluble in acid.
Ruby is red corundum, and its main colors are pink, red, purple and dark red, with red being the best. In particular, a pure ruby with a slight blue tone is the rarest, commonly known as "pigeon blood red". Natural rubies are very small, reaching 1 carat, and those larger than 5 carats are extremely rare. Up to now, the largest natural ruby has been found in Myanmar, with a mass of 3450 carats.
Sapphire generally refers to corundum of any color except ruby, but it should be distinguished by the previous color, such as yellow sapphire. Sapphire is preferably sky blue, bright and uniform in color. The output of sapphire is higher than that of ruby. A few carats are common, but more than 100 carats are also rare treasures. The largest sapphire in the world, with the mass of 19 kg, is produced in Sri Lanka.
If there are fine needle-like or thin-line rutile inclusions in ruby and sapphire crystals, if they are ground into hemispherical stones, six starlights will be produced, commonly known as "star ruby" (Figure 8-5) or "starlight sapphire".
2. Counterfeit rubies and sapphires
Artificial rubies and sapphires can be made by flame melting, but their growth lines are arc-shaped, which is different from the genuine linear growth lines.
Artificial starlight red, sapphire. The color of the original stone is poor, and the starlight bright line is uneven in thickness and distorted, so it cannot extend to the edge of the gem, while the artificial product is bright in color, and the starlight bright line is even in thickness and undistorted, extending to the edge of the gem.
Figure 8-5 Star Ruby (Rui Liu et al., 2007)
3. Substitutes for rubies and sapphires
The main substitutes are zircon, spinel and red glass. One kind of red spinel is easily confused with ruby, but their refractive index, fluorescence spectrum and other properties are different.
4. Origin of rubies and sapphires
Ruby and sapphire are mainly produced in Myanmar, Sri Lanka, Thailand, Kashmir, Tanzania, Kenya, Viet Nam, China and other countries and regions. Among them, Thailand is the most important producing area. As far as China is concerned, rubies are mainly produced in Yunnan and Qinghai. Sapphire is mainly produced in Changle County, Shandong Province. In addition, there are sapphires produced in Wenchang County, Hainan, Heilongjiang, Jiangsu, Fujian and other places. At present, high-quality rubies and sapphires are rare in the market, and 80% of rubies and sapphires in the world have been optimized.
(3) Emerald, the king of green (Figure 8-6, Figure 8-7)
Figure 8-6 Emerald Original Stone (Rui Liu et al., 2007)
Figure 8-7 Emerald Ring ()
Figure 8- 16 Spinel Twin (Jiang Yaofa et al., 2009)
The color of spinel is close to the red color of ruby, especially the high-quality products with large particles, few cracks and many inclusions are more expensive. In the early days, people often confused it with ruby, but their values were far from each other.
Blue spinel used to be confused with sapphire. When ground into a hemispherical plain stone, four or six starlight may appear.
2. The difference between ruby and sapphire
Spinel has a uniform color, preferably a medium depth, unlike the two-tone color bands in red and sapphire.
The transparency of spinel is based on the principle of not disturbing bright colors, unlike rubies and sapphires, which require high transparency.
Generally, the interior of spinel is relatively pure, and there are many fewer cracks, color bodies and defects than rubies and sapphires. If there is, its value will be greatly reduced.
Olivine (Figure 8- 17, Figure 8- 18)
Olivine is a group of minerals, there are 6 kinds, only forsterite and forsterite can become gems. The crystal is rarely columnar or short columnar, usually granular, with olive green, yellow green, emerald and other colors, transparent to translucent, with hardness of 6.5 ~ 7.0 and refractive index of 1.65 ~ 1.69. The biggest feature is color, with golden green and emerald as the best.
Fig. 8- 17 olivine crystal ()
Figure 8-20 Brown crystals associated with fluorite ()
Step 2 diversify
Crystal refers to colorless and transparent crystal, which is called "diamond" internationally.
Crystals can be polished into handicrafts, and crystal balls are the most famous because they conduct heat quickly and feel cold.
Amethyst is light purple to deep purple, which can be polished into diamond jewelry. It is a low-grade gem with poor transparency and can be used as an excellent raw material for carving handicrafts.
Barasuishou is pink, jade carvings are called hibiscus stones, and most of them are made into necklaces.
Smoke crystal, tea crystal, ink crystal, topaz, etc. They are mainly used to make glasses lenses, which have high hardness and are not frosted, but there are many fakes.
The colorless and transparent crystal with hair crystal contains needle-shaped, hairy and fibrous mineral crystals, which presents a unique aesthetic feeling and can be used as decorations.
3. Difference from glass
The hardness of crystal is 7, and the hardness of glass is 5-5.5; When you lick the tip of your tongue, the crystal feels cold and the glass feels warm; Observing with a magnifying glass, there are many bubbles and arcs in the glass, but not in the crystal; Looking through the crystal, the object has a ghost image, but the glass does not.
(1 1) Moonstone and Moonstone (Figure 8-2 1)
Figure 8-2 1 actinolite (http://222.66. 109.438+0)
Moonstone belongs to feldspar in mineralogy and is the most valuable gem of feldspar grade. Its hardness is 6, its relative density is 2.56 ~ 2.62, it is fragile, its refractive index is 1.520 ~ 2.525, and it has glass luster. Moonstone is usually colorless to white and transparent to translucent. From a certain point of view, it has luminous effect, almost all of which are the mixture of two (or more) feldspar, usually orthoclase and albite. The soft halo of moonstone, also called cryolite halo, is caused by the diffuse reflection of light by some small albite twins in orthoclase. The redder and thinner the bimorph, the brighter the moonlight. When processing, sometimes a bright band like "cat's eye" can be formed, showing light blue light waves.