The English name of crystal is Rockcrystal, also known as spar and crystal stone.
Crystal is a colorless and transparent timely crystal mineral. Its main chemical composition is silicon dioxide, which is a substance that "comes out of the uterus" with ordinary sand. When the crystal of silica is perfect, it is a crystal. Silica becomes agate after gelatinization and dehydration; Water-containing silica gel becomes opal after solidification; When the particle size of silica is less than several microns, chalcedony, flint and secondary quartzite are formed.
The crystal with perfect crystallization belongs to hexagonal system, which is often hexagonal prism. One or both ends of the cylinder are pointed, and many long cylinders are connected together, commonly known as the crystal family, which is beautiful and spectacular. The crystal of silicon dioxide is incomplete, and its shape can be described as varied. Going to Hainan Crystal Exhibition Hall can be an eye-opener: in addition to the common long columns, there are sword-shaped, plate-shaped, short-column and double-column ones. Some are less than half a catty, and some weigh more than 300 kilograms.
1824, an Austrian mineralogist named Frish Moss extracted 10 varieties from many minerals, and measured their relative hardness through scientific experiments, from which it was concluded that the crystal hardness was Mohs 7. Although the American National Bureau of Standards later used and popularized the more scientific Knoop hardness tester, jewelers in many countries in the world are still used to using Mohs hardness meter.
Well-crystallized crystals usually have a good herringbone fracture with parallel ridges; In amethyst and heat-treated topaz, most of them are uneven flaky cracks.
Crystal specific gravity: 2.56-2.66g/cm3.
This means that the weight of a certain volume of crystals is 2.56-2.66 times that of the same volume of water. The density of bulk variant crystals may be slightly higher.
Crystal stripes: colorless.
Stripes, commonly known as colors, are the result of human eyes' perception of light with a certain wavelength.
The transparency of a crystal is related to the quality and quantity of light passing through it. The standard of transparency is that the reflected image can be clearly seen when the light passes through a crystal slice or slice with a thickness greater than 1 cm. If the bottom image is not clear enough and only the outline is seen, it is translucent.
Crystal luster: glass luster. This is true for polished surfaces and cracks.
Gloss refers to the optical characteristics of reflected light on the surface of a gem. Crystal will not reflect beautiful star stripes like starlight sapphire and starlight gemstone, nor will it give off light blue wave luster like moonstone, nor will it flicker like opal.
To observe the luster of the crystal, you can hold it in your hand and look at the surface reflection with the light of a lamp or a window. The brightness of transparent crystal is related to its luster.
The refractive index of crystal: 1.544- 1.553, which is almost within this range.
Refractive index is the ratio of sine of incident angle to sine of refraction angle when light penetrates into gem crystal from air and produces refraction phenomenon.
Crystal refractive index: 0.009 (maximum), very stable.
Optical characteristics of crystal: uniaxial crystal positive light.
Crystal dispersion: 0.0 13.
Dispersion means that the refractive index of a gem changes with different illumination light. For example, the refraction of red light by diamonds is 2.405; 2.427 is the green light; Purple light is 2.449.
The melting point of the crystal is 17 13 degrees Celsius. Its fragility was found in the experiment. If the crystal is baked in the flame of a flame burner, it is easy to break unless it is well protected and slowly cooled. This kind of temperament has been thoroughly understood by the ancients. "Introduction to Natural History" reminds: "Anyone who uses crystal objects should not pour hot soup, that is, if the powder is broken, it will crack."
Another temperament of crystal is that it is afraid of alkali and acid (except hydrofluoric acid), which is determined by the characteristics of silicon oxide.
Gems such as agate often give off a special smell when heated, rubbed, blown or hit, which reminds people of garlic, horse meat, radish, pine and so on. However, the crystal has no peculiar smell in the above case.
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Chemical composition and properties of crystals;
The chemical formula is silicon dioxide. Pure colorless and transparent crystal is a variety of seasonable. Its chemical composition contains 46.7% silicon and 53.3% oxygen. Many colors appear because they contain different impurities or are mechanically mixed. Purple and green are caused by iron (Fe2+) ions, purple can also be caused by titanium (Ti4+), and other colors are caused by color centers. The crystals contain sand. Hair crystals contain inclusions of hair-like needle-like minerals visible to the naked eye. Those containing manganese and iron are called amethysts. Iron (golden or lemon) is called topaz; Rose color containing manganese and titanium is called rose season; Smoke color is called smoke crystal; Brown is called tea crystal; Black and transparent are called ink crystals; Those light green ones are called pith.
Crystal structure and morphology:
It belongs to the triangular system. Crystal is prismatic, hexagonal cone, with horizontal stripes on the cylinder, and there are often angular stripes in amethyst. In nature, crystals are often produced in groups with beautiful shapes.
Physical properties of crystals:
The crystals are colorless, purple, yellow, green and smoky. It is glassy, transparent to translucent, hard and brittle, with a specific gravity of 2.65. No cleavage. Shell fractures also have good herringbone fractures with equal ridges. Amethyst has obvious dichroism, while topaz and tea crystal have weak dichroism. Light emitting crystals have strong phosphorescence. Green gold placer crystal emits gray-green fluorescence under long-wave and short-wave ultraviolet irradiation.