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Crystal (crystal mineral)

Rock crystal is a rare mineral, a kind of gemstone, quartz crystal, which belongs to the quartz family in mineralogy. The main chemical component is silicon dioxide, and the chemical formula is SiO2.

When pure, it forms colorless and transparent crystals. When it contains trace elements Al, Fe, etc., it is pink, purple, yellow, brown, etc. The irradiated trace elements form different types of color centers, resulting in different colors, such as purple, yellow, brown, pink, etc. Minerals containing associated inclusions are called inclusion crystals, such as hair crystals, green ghosts, red rabbit hair, etc. The inclusions are rutile, tourmaline, actinolite, mica, chlorite, etc.

Rock Crystal is a kind of Quartz crystal mineral. Its main chemical component is silicon dioxide and its chemical formula is SiO2. Western countries believe that as long as it is transparent, it is crystal (Crystal), so the term crystal includes colorless and transparent glass (K9, ordinary glass blue), as well as natural crystal ore. The ancient Chinese crystal names are more than ten kinds of names, such as water essence, water green, water jade, spar, etc. Therefore, in order to facilitate the distinction, the international term (Rockcrystal) is usually used to refer to natural crystals. The well-developed single crystals are hexagonal pyramids, so they are usually massive or granular aggregates, generally colorless, gray, and milky white. When they contain other mineral elements, they are purple, red, smoke, tea, etc. [2].

When the crystal of silicon dioxide is perfect, it is crystal; when the crystal is not perfect, it is quartz: after silica gelation and dehydration, it is agate; when the water-containing colloid of silicon dioxide is solidified, it becomes opal; when the crystal grains of silicon dioxide are smaller than a few microns, it is composed Chalcedony, flint, secondary quartzite.

Chemical composition: silicon dioxide, the chemical composition contains Si—46.7% and O—53.3%. It presents a variety of colors due to the presence of different trace elements or color centers. Mineral composition: goethite, hematite, rutile, magnetite, tourmaline, garnet, mica, chlorite, etc. form inclusion crystals, such as hair crystals, titanium crystals, green ghosts, etc. Formation of inclusions containing hair-like needle-like minerals that are visible to the naked eye. Those with manganese and iron are called amethyst; those with iron (golden or lemon) are called citrine; those with manganese and titanium are called rose quartz, which is pink crystal; those with smoke are called smoky crystal; those with brown are called rose quartz. Called citrine; black and transparent ones are called smoky crystals.

Optical properties Color: colorless, light to dark purple, light yellow, medium to dark yellow, light to dark brown, brown, green to yellow-green, light to medium pink. Amethyst: light to deep purple. Citrine: light yellow, medium to dark yellow. Blue crystal: light blue, dark blue. Almost all blue crystals are artificially synthesized.

Smoke crystal: light to dark brown, brown. Since Al3+ replaces Si4+ in the composition, [AlO4]4-color center is produced after irradiation.

Green crystal: green to yellow-green. The color formation is related to Fe2+. Naturally formed green crystals are almost non-existent in the market. It is usually an intermediate product formed during the heating of amethyst into citrine. Hibiscus stone: light to medium pink, with a lighter tone. It is usually pink due to the trace amount of titanium (Ti). Can have a transmissive starlight effect. Hair crystals: colorless, light yellow, light brown, etc., can be golden, brown and red due to rutile, gray-black when it contains tourmaline; gray-green when it contains sunstone. Luster: Glass luster. The fracture surface is greased and shiny. Luster refers to an optical property of the surface of a gemstone to reflect light. To observe the luster of the crystal, you can hold it in your hand and see the reflection on the surface with the light from the light or the window. The brightness of the transparent crystal is related to the strength of the luster. Transparency: The transparency of a crystal is related to the quality and quantity of light passing through it. When the light passes through crystal shards or flakes with a thickness of more than 1 cm, the reflected image can be clearly seen. If the bottom image is not clear enough and only the outline is visible, it is translucent. Refractive index (RI): 1.544-1.553, almost within this range. (The refractive index is the ratio of the sine of the incident angle to the sine of the refraction angle when light penetrates into the gem crystal from the air and produces refraction.) Double refraction rate (DR): 0.009 (maximum), this value is very stable.

Dispersion value: 0.013. Dispersion means that the refractive index of the gemstone varies to a certain extent with the different illumination light. For example, diamond refracts 2.405 to red light; 2.427 to green light; and 2.449 to purple light.

Optical: One-axis crystal( is optical. The uniaxial crystal interferogram seen under orthogonal polarized light is unique. Its black cross arms do not reach the center and form a hollow pattern, commonly known as bull's eye interferogram. The center part is usually light green or light pink. Pleochroism: Colorless crystal has no pleochroism. Colored crystals have weak to strong pleochroism. They are manifested in different shades of body color.

Mechanical properties Cleavage: No cleavage. The so-called cleavage refers to the property that when a mineral is hit, it splits regularly in a certain direction to form a smooth plane. According to the degree of cleavage, it can be divided into five categories: extremely complete cleavage, complete cleavage, medium cleavage, incomplete cleavage and no cleavage. Crystals belong to no cleavage.

Fracture: Conchoidal. Fracture is also called breach. It refers to the irregular fracture of the mineral after being hit, and the unevenness of the fractured surface is called a fracture. According to the shape of the fracture, it can be divided into conchoidal and serrated.

Hardness: Mohs hardness 7, which is Mohs hardness, which is equivalent to the hardness of steel files. In 1824, an Austrian mineralogist named Frisch Moss extracted 10 species from many minerals and measured their relative hardness through scientific experiments. From this, the crystal hardness was 7 Mohs. Although the American National Bureau of Standards later used and promoted the more scientific Knopp hardness tester, jewellers in many countries in the world are still accustomed to the Mohs hardness scale.

Density (specific gravity SG): 2.66 (0.03, 0.02) g/cm3. This means that the weight of a certain volume of crystal is 2.56-2.66 times the weight of the same volume of water. The crystal density of the block variant may be slightly higher.

Piezoelectricity: The crystal will generate electric charge when it is under pressure; on the contrary, when it is under voltage, the crystal will produce high-frequency vibration. Crystal has the ability to transfer pressure and charge to each other, which is called piezoelectricity. Streak color: colorless. The color of mineral powder is called streaks. It can eliminate false colors, weaken other colors, and retain self-color. It is one of the more reliable identification characteristics than the color of minerals.

Melting point: The crystal melting point is 1713°C. Its characteristic of being fragile when heated was discovered in experiments. Place the crystal in the flame of a flamethrower and burn it. Unless it is well protected and cooled slowly, the crystal is easy to break. The ancients have already figured out this temperament.