1. Mineral name
The mineral name of this crystal is Yingshi. At that time, a kind of transparent single crystal that can be used as a gem is collectively called crystal in the jewelry industry.
2. Chemical composition
The chemical composition is silicon dioxide (SiO2), which may contain trace elements such as titanium, iron and aluminum. These trace elements cause color centers and make crystals appear different colors.
3. Crystal system and crystallization habit
Tripartite system. Mostly columnar habits. Common simplex includes hexagonal column M, rhomboid R and Z, triangular bipyramid S and triangular polyhedron X (see figure 16-4- 1). The rhombohedral R is generally more developed than Z. When the rhombohedral R and Z are equally developed, it is a pseudo-hexagonal bipyramid in appearance. There are stripes and polygonal etched images on the cylindrical surface of columnar crystals.
The common twins in crystal are Youfen Twin, Brazil Twin and Japan Twin.
Figure 16-4- 1 Crystal
The shape to the left; B- right shape
4. Optical characteristics
(1) color: the color of the crystal can be colorless, purple, yellow, pink, green, blue and brown to black in different degrees.
(2) Gloss and transparency: glass luster, and the fracture surface may have grease luster. Transparency, with the increase of inclusions or the deepening of colored crystal color, transparency decreases.
(3) luminosity: uniaxial ortholuminosity. The interference pattern of uniaxial crystal seen under orthogonal polarization is unique, and its black cross arm does not reach the center, forming a hollow pattern, commonly known as bull's-eye interference pattern. The central part is usually light green or light pink.
(4) refractive index and birefringence: refractive index 1.544 ~ 1.553, and birefringence 0.009. The deviation is 0.0 13.
(5) Polychromaticity: Colorless crystals have no polychromatic properties. Colored crystals have a variety of colors from weak to strong, showing different shades of body color. Generally speaking, the darker the lower body color, the more obvious the multicolor.
5. Mechanical properties
(1) Cleavage: no cleavage. There is a typical shell fracture.
(2) Hardness: Mohs Hardness 7
(3) Density: 2.65g/cm3.
6. Piezoelectric
Crystal crystal will produce charge when it is pressed; On the contrary, when the crystal is subjected to voltage, it will produce high-frequency vibration. Crystals have the property that pressure and charge can be transferred to each other, which is called piezoelectricity.
Second, the types of crystals.
According to the color, crystals can be divided into different gem varieties: crystal, amethyst, topaz, amethyst, smoky crystal, black crystal, hibiscus stone, and occasionally green quartz and blue quartz. According to the special optical effect, it can be divided into two varieties: starlight and quartz cat's eye.
1. transparent
Especially colorless and transparent single crystal time.
Crystals can be rich in inclusions, including negative crystal inclusions, fluid inclusions and solid inclusions.
Negative crystal inclusions often appear in crystals, which are irregular, dispersed or densely distributed, foggy, flocculent or slag-like. Some are so small that they can only be seen at high magnification. Most negative crystals are filled with gas and liquid and become fluid inclusions. There are many kinds of solid inclusions, the most common nonmetallic mineral inclusions are rutile, tourmaline and actinolite, and others are calcite, mica and cassiterite. Metal mineral inclusions include hematite, goethite, limonite, ilmenite, brookite, wolframite and natural gold. Inclusions of rutile, tourmaline and actinolite are usually fine needles and fibers, and their orientation and shape are like hair. This kind of crystal is usually called hair crystal.
2. Purple
Also known as amethyst. Transparent to translucent purple crystal. The color range can be from nearly colorless to lavender to purplish red, and the distribution is often uneven, showing spots or stripes. Having dichroism (different shades of blue-purple to purple). Amethyst is the most popular single crystal in various colors. For a long time, it has been used as an ornament and amulet. It is believed that it can refresh the mind, relieve alcoholism and detoxify, increase wisdom and ensure peace. Amethyst was once called love stone and bishop stone in the west. The crystal habit is mainly rhombohedral, and columnar crystals are rare. Most of them gather in holes, and the darker ones are just the top of the crystal, which often turns down into crystals or milky white. In amethyst, there are linear, angular and characteristic banded structures called "tiger stripes" or "zebra stripes", as well as irregular, negative crystal gas-liquid inclusions and needle-like inclusions of goethite, lepidolite and rutile. It is believed that the purple color of amethyst is the result of natural or artificial irradiation of topaz. Amethyst will turn into yellow crystal after heat treatment, and sometimes it will produce transparent green time after heating. At present, there are many amethysts on the market as synthetic products.
3.topaz
Also known as "topaz". Transparent yellow single crystal timing. Yellow, orange, brown and light red are related to trace Fe3+, which is the result of charge transfer between O2- and Fe3+. Usually dichroism is obvious. It can contain the same inclusions as amethyst, such as "tiger pattern" and ribbon. Topaz is rarely produced in nature, and is mostly related to amethyst and crystal strings. Some of the popular topaz in the market are heat-treated amethyst, but most of them are synthetic.
4. Purple
Also known as "two-color crystal", it means that purple and yellow appear in the same crystal, and the two colors are clearly defined. It is believed that this is caused by twin phenomenon, and purple and yellow appear in the R plane and Z plane of twin monomer respectively. Experiments show that amethyst can be produced occasionally when heated to 350 ~ 400℃. The main producing area of natural amethyst is Bolivia. At present, Russian hydrothermal method has successfully synthesized amethyst, even amethyst-yellow-green time.
5. Smoke crystals
Smoke yellow to dark brown seasonal crystal, when there is a black tone, it is called "ink crystal". The color distribution is uneven, which can be thin bands or patches. The timely smoke color is due to the existence of impurity Al3+. However, the presence of Al3+ ions alone is not enough to produce a brown color. It takes a long time of natural or artificial irradiation to extrude electrons, form electron color centers, and cause absorption in the range of ultraviolet to visible light. When heated, it can weaken brown or turn brown, then turn green and yellow until it is colorless. Re-irradiation can restore or deepen the brown color. Smoke crystals have obvious dark brown/light brown dichroism. Translucent to opaque. Common gas-liquid two-phase inclusions with irregular shape and negative crystal morphology, as well as mineral inclusions such as tourmaline and rutile. At present, many smoke crystals on the market are irradiated and synthesized.
6.hibiscus stone
Also known as "rose in season". Light red to rose red, its color can be from near white to deep rose red. Although a few hibiscus stones are transparent and clean and can be cut into faceted gems, most of them are foggy and contain a lot of tiny inclusions and cracks. Hibiscus is concentrated in pegmatite vein core, and there is usually no obvious boundary between single crystals. Many hibiscus stones contain oriented rutile needle inclusions. Seen from a certain direction with transmitted light, we can see the starlight effect, which belongs to transmitted starlight. Using this characteristic, hibiscus stone is sometimes made into imitation star sapphire. Sillimanite inclusions in hibiscus sometimes lead to starlight effect. At present, it is believed that the color of hibiscus is the result of charge transfer between Ti4+ and Fe2+, which may be related to irradiation, but some people think that it is caused by manganese and titanium. Deep hibiscus stone can be two colors, but it is difficult to detect when it is light.
7. Green seasonality
It is usually green, because colorless crystals contain a lot of mineral inclusions such as chlorite. Poor light green is produced in Brazil. At present, the green time seen in the market is mostly the intermediate product in the process of heating amethyst into yellow crystal.
8. Blue is in season
It is usually colored by a large number of tiny light blue rutile needles. Natural blue is always overcast and covered with fine needles. The blue time seen in the market is mostly transparent cobalt color synthesis time with characteristic cobalt spectrum.
9.quartz cat's eye
It is a single crystal with parallel asbestos fibers, which will produce cat's eye effect when it is cut into arc gems. Inclusion and cat's eye effects are usually thicker than emeralds. When parallel rutile inclusions appear in the stress, they can also be processed into cat's eye effect.
10. Starlight should be timely
In addition to hibiscus, crystals containing rutile needles sometimes show six stars.
1 1. Crystallization, "phantom crystal"
Various strains often contain inclusions such as rutile, tourmaline, actinolite, chlorite and stibnite. Most of them are needle-shaped, fibrous, aquatic, stone-flowered and hairy. This kind of timely crystal is called "hair crystal". When the inclusions are arranged along the growth plane, the phantom of single-layer or multi-layer crystals is formed, which is called "phantom crystal".
Third, the identification of crystals.
The identification of crystals is mainly through measuring density, refractive index and birefringence, and observing optical characteristics and inclusions. Gems that are easily confused due to similar refractive index and color include andalusite, cordierite and feldspar.
1. The difference between crystal and andalusite
Amethyst and topaz are easily confused because their refractive index and color are similar to those of purple and yellow andalusite. See table 16-4- 1 for the distinguishing method.
Table 16-4- 1 the difference between crystal and andalusite
2. The difference between amethyst and cordierite
Although the birefringence of amethyst is similar to cordierite (0.008 ~ 0.0 12), there are obvious differences in color and polychromatic. The color of cordierite is purple-blue ~ blue, and the purple of amethyst rarely appears. Cordierite is obviously polychromatic and visible to the naked eye, and different colors can be seen from different directions. Amethyst is the same color with different shades (blue and purple to purple shades are different). In addition, amethyst is a uniaxial crystal with a bull's-eye interference pattern, while cordierite is a biaxial crystal.
3. The difference between crystal and feldspar
Colorless crystal and colorless feldspar are very close in refractive index and density, so it is difficult to distinguish them. The main method is to enlarge the inspection. Feldspar has two groups of polar perfect cleavage. Microscopically, a centipede-like inclusion or a thin and straight texture formed by the intersection of two cleavage groups can be seen, while the crystal has no cleavage development, only intermittent and irregular cleavage can be seen.
Fourthly, the optimization of crystal processing
There are methods such as irradiation, heat treatment, dyeing and coating.
radiation
Any colorless crystal can become smoke crystal after irradiation, and its color ranges from black and brown to red, yellow or light green. Iron-containing amethyst can be produced after timely irradiation. Radiation can also produce green, yellow and pink. These colors are stable under light, and some will change color or fade after heat treatment.
2. Heat treatment
Heating can make the color of smoke crystal lighter or lighter, which depends on temperature and heating time. Yellow-green color and blue color can be produced in the fading process of heat treatment. Heating amethyst can make its color lighter, heating to 450℃ can produce yellow, and at higher temperature (500 ~ 575℃), it will produce orange or brownish red caused by iron oxide. Many topaz on the market are heated by amethyst. Some amethysts produce green color when heated to 400 ~ 500℃. Some of them can also produce milky white appearance after high temperature heat treatment (500℃ for 24 hours) to imitate moonstone.
dye
After the crystal is heated, it is quickly put into cold water, resulting in a large number of cracks. The cracks are filled with air, which leads to the halo effect. The time produced by this method is called "flint" or "cracked time". Sometimes pigments are added to water to dye gems to imitate rubies or emeralds.
paint
In recent years, a new method is to coat a very thin and transparent pure gold film (sometimes platinum film or silver film) on the crystal surface by plasma deposition and vacuum spraying technology, so that its surface is blue to blue-green, accompanied by copper-like surface halo. This treatment method and effect are called "water aura". Another example is timely and chalcedony, which are sprayed with titanium to form a titanium oxide film and sold in the market under the name of "titanium dioxide gem". These coatings can obviously improve the color and luster of the gemstone, still maintain the transparent appearance and improve the durability without affecting other gemological properties of the gemstone.
Verb (abbreviation for verb) synthesizes crystals.
Because the electronics industry needs pure and single crystal timing, after years of efforts, spezia first synthesized single crystal timing by hydrothermal method in 1908. Synthetic timepieces are mostly colorless. At present, they are mainly used for industrial purposes, but they are also used in jewelry industry, especially colored timepieces. Hydrothermal method uses a sealed container-autoclave. Crusts of raw rock crystals are placed at the bottom of the autoclave, and the autoclave is filled with 4% sodium hydroxide with a filling degree of 60% ~ 80%. The heating temperature at the bottom of the autoclave reaches 390℃, while the temperature at the top is lower, which is 330℃. The pressure reaches 1.5 kPa. The raw materials are separated in ionic state at the bottom of the autoclave and grow on the upper seed crystal after migration. After 20 days of growth, a batch of 32 kilograms of raw materials can grow 700g crystals with a thickness of 5cm on 40 seed crystals with a size of 4 cm×15 cm×1mm. When the growth rate is 65438±0mm per day, clean crystals can be obtained. By adding some additives or subsequent irradiation, we can obtain various monochromatic time, even two-color time. Russian scientists are in a leading position in this field. In addition to the original varieties, in recent years, they have successfully synthesized hibiscus, amethyst, yellow-green time, amethyst-amethyst-green time, and amethyst has started commercial production.
Artificial crystal is difficult to distinguish from crystal stone. The following signs help to identify:
The (1) synthetic crystal has typical mountain-shaped features on some crystal planes.
(2) Some synthetic crystal products have seed crystals. It has obvious boundary and color difference with the growing crystal. Very fine stress cracks and nail inclusions often appear near the seed crystal.
(3) Bread crumb inclusion is a typical characteristic of synthetic timing. They are augite or timely microcrystal nuclei, or from undissolved raw materials. When the crystal growth conditions are stable, bread crumbs are very scarce. When the crystal growth conditions are unstable, bread crumbs can appear in large quantities and run through the whole crystal in one or several layers parallel to the seed crystal direction. Attention should be paid to distinguish it from gas-liquid inclusions in rock crystals under high magnification.
For those very pure ornaments with few growth traces, infrared spectrometer can be used to distinguish natural and synthetic crystals by measuring the absorption peaks of OH- and H2O in crystals. Natural colorless crystals are characterized by absorption peaks of 3595cm- 1 and 3484cm- 1, while synthetic colorless crystals are characterized by absorption peaks of 3585cm- 1 and 5200cm- 1. Natural amethyst has an obvious absorption peak at 3545cm- 1, while synthetic amethyst has only a weak peak.
Six, imitation crystal
The imitation of crystal is mainly glass. At present, there are mainly glass balls, glass necklaces and dark brown glass lenses in China market. Glass is an amorphous material, and it is not difficult to distinguish it from crystal by detecting its optical characteristics.
Seven. Brief introduction to the generation and output of crystal deposition
Crystals are mainly produced in veins of magmatic hydrothermal deposits and pegmatite deposits, and mostly developed in the core of pegmatite and crystal caves in veins. Almost all parts of the world have crystal output. Amethyst is mainly produced in Brazil, Uruguay and Russia, and other colored crystals are mainly produced in Madagascar, the United States and Myanmar. China has a large number of high-quality colorless crystals.
Eight, use
(1) single crystal (colorless crystal) is often used to make piezoelectric response in industry and is widely used in electronic industry.
(2) Colorless and colored crystals (natural and synthetic) are commonly used in jewelry industry.
(3) It is also widely used in ceramic industry and glass industry.