There are more than a dozen common gems. Gems, especially high-grade gems, are expensive, which is by no means affordable for low-income people. Common gemstones are briefly described as follows:
(1) Diamond-the king of gemstones (Figure 8-2)
Figure 8-2 Blue diamond (Liu Rui et al., 27)
The scientific name of the mineral is diamond, which becomes diamond after grinding. Mohs hardness is 1, which is the hardest substance in the world at present, and its polished surfaces 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, when the light shines, it flickers, which is extremely charming and has a strong "fire". The color is colorless, but the dark and transparent ones are treasures, and the light blue ones are the best. The chemical properties are extremely stable. Defects are too brittle, easy to break, and not resistant to high temperature above 8℃. The output is small, only about 2% 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, rhombus, cube, etc. On the crystal surface, there are often inverted triangular pits. People have used diamonds for more than 2, years, but the particles are all small, less than 2, with a mass greater than 1 carats, less than 5 with a mass greater than 2 carats, and only 2 with a mass greater than 5 carats, which is extremely rare. The world's largest diamond, Cullinan, was discovered in 195, with a mass of 3.16 carats, which is equivalent to the fist size of an adult man.
diamonds smaller than .24 carats are small diamonds, those between .25 and .99 carats are medium diamonds, and those above 1 carat are large diamonds. People divide a carat into 1 parts, each part is 1 minute.
rough diamond: because of its extremely high hardness, it can be identified by scoring or thermal conductivity meter;
finished diamond (identified by naked eyes): it has a strong affinity for grease. When you touch the 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 dispersed, it will be a fake diamond.
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 large.
at present, 27 countries in the world produce diamonds. Diamonds were first discovered in India. South African diamonds are famous for their large size. More than 1,9 diamonds over 1 carats have been found in the world, 95% of which are produced in South Africa. Australia is the number one producer with an annual output of 7, tons of diamonds. 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 rough stone (Liu Rui et al., 27)
Figure 8-4 Starlight Sapphire (Liu Rui et al., 27)
1. Features < p
Ruby is red corundum, and the main colors are pink, bright red, purplish red and dark red, with bright red being the best. Especially a pure red ruby with a slight blue tone is the rarest, commonly known as "pigeon blood red". Natural rubies are very small, reaching 1 carat is rare, and those larger than 5 carats are extremely rare. So far, the largest natural ruby is found in Myanmar, with a mass of 3,45 carats.
Sapphire generally refers to corundum of any color except ruby, but it should be distinguished by a color in front of it, such as yellow sapphire. Sapphire is best with bright sky blue and uniform color. The output of sapphire is higher than that of ruby. A few carats are common, but more than 1 carats are also rare treasures. The world's largest sapphire weighs 19 kilograms and is produced in Sri Lanka.
If there are fine needle or fine thread rutile inclusions in ruby and sapphire crystals, if they are ground into hemispherical stone, they will produce six starlight, commonly known as "star ruby" (Figure 8-5) or "starlight sapphire".
2. Counterfeit products of red and sapphire
Artificial red and sapphire can be made by flame melting, but their growth lines are arc-shaped, which is different from the straight growth lines of genuine products.
artificial starlight red and sapphire. The original color is relatively poor, the starlight bright line is uneven in thickness, and the distortion is not straight, so it can't extend to the edge of the gem, while the artificial product is very bright in color, and the starlight bright line is even in thickness without distortion and extends to the edge of the gem.
Figure 8-5 star ruby (Liu Rui et al., 27)
3. Substitutes for ruby and sapphire
Substitutes mainly include zircon, spinel and red glass. There is a kind of red spinel that is easily confused with ruby, but their refractive index, fluorescence spectrum and other properties are different.
4. Origin of ruby and sapphire
Ruby and sapphire are mainly produced in Myanmar, Sri Lanka, Thailand, Kashmir, Tanzania, Kenya, Viet Nam, China and other countries and regions in the world. 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 8% of the rubies and sapphires in the world have been optimized.
(3) King of Green-Emerald (Figure 8-6 and Figure 8-7)
Figure 8-6 Emerald Raw Stone (Liu Rui et al., 27)
Figure 8-7 Emerald Ring ()
Figure 8-16 Spinel Twin (Jiang Yaofa et al., 2 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. Differences from rubies and sapphires
Spinels are uniform in color, with a medium depth being preferred, unlike rubies and sapphires, which often have ribbons with different shades.
the transparency of spinel is based on the principle of not hindering the vividness of color, unlike rubies and sapphires, which require high transparency.
generally, the interior of spinel is relatively pure, and there are fewer cracks, color bodies and defects than rubies and sapphires. If there are any, its value will be greatly reduced.
(9) Olivine (Figure 8-17, Figure 8-18)
Olivine is a group of minerals with ***6 species, and only forsterite and forsterite can become gems. Crystals are rare columnar or short columnar, usually granular, with olive green, yellow green, emerald and other colors, transparent to translucent, with hardness of 6.5 ~ 7. and refractive index of 1.65 ~ 1.69. The biggest feature is color, with golden green and emerald as the best.
figure 8-17 olivine crystal ()
figure 8-2 brown crystal is associated with fluorite ()
2. variety
crystal refers to colorless and transparent crystal, and high-grade crystal is called "diamond" internationally.
crystals can be polished into handicrafts, and the crystal ball is the most famous one, because it conducts heat quickly and feels cold to the touch.
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 crafts.
Barasuishou is pink, and jade carving is called hibiscus stone, which is mostly made into necklaces.
Smoke crystals, tea crystals, ink crystals and topaz are mainly used as spectacle lenses, which have high hardness and do not abrade, but there are many fakes.
there are needle-like, hair-like and fibrous mineral crystals in the colorless transparent crystal with hair crystal, which shows a unique beauty and can be used as decoration.
3. Difference from glass
The hardness of crystal is 7, and that of glass is 5-5.5; When you lick the tip of your tongue, the crystal feels cold, while the glass feels warm; Observing with a magnifying glass, there are many bubbles and arc lines in the glass, but not in the crystal; Seeing through the crystal, the object has a double image, but the glass does not.
(11) Moonstone and actinolite (Figure 8-21)
The actinolite in Figure 8-21 (http://222.66.19.21)
Moonstone belongs to feldspar in mineralogy and is the most valuable feldspar-grade gem. Its hardness is 6, its relative density is 2.56 ~ 2.62, it is brittle, its refractive index is 1.52 ~ 2.525, and it has glass luster. Moonstone is usually colorless to white, transparent-translucent. When viewed from a certain angle, there is a luminous effect, which is almost always a mixture of two (or more) types of feldspar, usually orthoclase and albite. Moonstone's gentle halo, also known as cryolite halo, is produced by diffuse reflection of light by some fine albite bimorphs in orthoclase. The redder and thinner the bimorph is, the brighter the moonlight is. When it is processed, it can sometimes form a bright band like a "cat's eye" and present a light blue light wave.