Crystal is a colorless and transparent large-scale 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 silicon dioxide crystal 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 chemical formula is silicon dioxide. Pure colorless and transparent crystal is a variety of seasonable. The chemical composition contains 46.7% silicon and 53.3% oxygen. Because it contains different mixtures or mechanical mixtures, it has many colors. 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 sandy and fragmented goethite, hematite, rutile, magnetite, garnet and chlorite. Hair crystals are formed by inclusions containing hairy needle-like minerals visible to the naked eye. Containing manganese and iron is called amethyst; 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; The light green one is called stone pulp.

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 emit 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.

Physical properties of crystals:

1824, an Austrian mineralogist named Frish Moss extracted 10 varieties from many minerals, and determined their relative hardness through scientific experiments, from which 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 tester.

The crystal with perfect crystallization belongs to hexagonal system, often in hexagonal prism shape. The cylinder is pointed at one end or at both ends, 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. Go to Hainan Crystal Exhibition Hall, and you will be an eye-opener: in addition to the common long columns, there are sword-shaped, plate-shaped, short columns and double cones. Some are as small as fingers, and some are as big as boulders; Some are less than half a second, and some weigh more than 300 kilograms.

Crystal is colorless, purple, yellow, green and smoky. Glass luster. Transparent to translucent. Hardness 7. Sexually fragile. The specific gravity is 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. It has cat's eye, rainbow and placer gold effects. The crystal is piezoelectric.

Crystal structure and morphology

It belongs to the tripartite crystal system. The crystal is prismatic, with a hexagonal cone, the cylinder has horizontal stripes, and amethyst often has angular stripes. In nature, crystals are often produced in groups with beautiful shapes. .

Well-crystallized crystals usually have a good herringbone fracture with parallel ridges; In amethyst and heat-treated topaz, most of them are uneven sheet fractures.

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. Bulk crystals may have a slightly higher density.

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 transparency standard is that when light passes through crystal fragments or slices with a thickness greater than 1 cm, the reflected image can be clearly seen. If the bottom image is not clear enough and only the outline is seen, it will be translucent.

Crystal luster: glass luster. This is true for both polished and fractured surfaces.

Gloss refers to the optical characteristics of reflected light on the surface of a gem. Crystal does not reflect beautiful starlight stripes like starlight sapphire and starlight sapphire, nor does it shine with light blue waves like moonstone, nor does it shine with colors 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.

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 the change of 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. In the experiment, it was found that it was brittle when heated. The crystal is baked in the flame of a flame burner. Unless it is well protected and cooled slowly, the crystal is easily broken. This kind of temperament has been thoroughly understood by the ancients. Introduction to Natural History reminds us: "Anyone who uses crystal objects should not pour hot soup into it, that is, the powder will crack like a broken one."