Jade belongs to jade. The essential difference between jadeite and precious stones is that jadeite is a polycrystalline aggregate, while diamonds, rubies and sapphires are single crystals. Single crystal means that a gem has a relatively stable refractive index, hardness and density, while polycrystalline aggregate means that the refractive index, hardness and density of jade are not a fixed value, but a changing range. Among jadeite, there are pyroxene minerals such as jadeite and omphacite, and non-pyroxene minerals such as albite and amphibole. The content of these minerals is not only unstable, but also the particle size and embedding degree of these minerals have changed to some extent. The characteristics of jadeite in mineral composition and structure determine the uniqueness of its basic attributes such as color, transparency, density and hardness (pictured).
These are emeralds.
1, mineral composition
In a narrow sense, jadeite refers to a polycrystalline aggregate with technological value and jadeite as the main mineral component. However, in recent ten years, there has been an aggregate from Myanmar with sodium chromite and omphacite as the main mineral components, also named after jadeite, which has been recognized by consumers. Because the aggregate of sodalite and omphacite has gem characteristics similar to that of jadeite aggregate, a broad definition of jadeite is produced. Jade in a broad sense refers to a polycrystalline aggregate with technological value, which is mainly composed of jadeite, sodium chromate or omphacite.
Ouyang Qiumei clearly pointed out that the main mineral composition of jadeite must be alkaline pyroxene, and there are three kinds of minerals involved in the naming of jadeite, sodalite and omphacite, and only when the total content exceeds 50% can it be called jadeite (Ouyang Qiumei's Qiumeizhi Cuisine P62). According to the main mineral composition, jadeite can be divided into jadeite, sodium chrome pyroxene and omphacite (pictured). There are some differences in the physical properties of these three minerals, especially the differences in color and refractive index, which lead to different appearances of jadeite.
According to the main mineral composition, jadeite can be divided into three categories, which are mainly composed of different pyroxenes.
Besides pyroxene minerals, jadeite may also contain amphibole minerals in different amounts, such as tremolite, actinolite, amphibole and albite, chromite, magnetite, hematite and limonite.
2. Chemical composition
Due to the uncertainty of mineral composition of jadeite, its chemical composition is also uncertain. The chemical composition of jadeite determines its mineral composition. The main mineral components of jadeite are jadeite, sodalite and omphacite, so the chemical composition of jadeite depends on the content of these three minerals.
The chemical composition of jadeite is NaAlSi2O6, which often contains trace impurities such as chromium, iron, manganese, calcium, magnesium and titanium. The chemical composition of sodalite is NaCrSi2O6. The chemical composition of omphacite is (Ca, Na)(Mg, Fe, Al)Si2O6.
Therefore, the main chemical components of jadeite can be regarded as "eight-treasure porridge" composed of three terminal components: NaAlSi2O6, NaCrSi2O6, (Ca, Na)(Mg, Fe, Al) SiO6 in any proportion. When the main mineral is jadeite (NaAlSi2O6), it is jadeite in a narrow sense. When the main mineral is NaCrSi2O6, it is the so-called Gan Qing jadeite. When the main mineral is omphacite (Ca, Na)(Mg, Fe, Al)Si2O6, it is called Cui Mo.
3. Structure
Jade is a mineral aggregate. The particle size, shape and combination of minerals in jade are called the structure of jade, which is called texture in the industry. The structure of jade determines its texture, transparency, luster, hardness, density and other characteristics, which is the most important index to determine the quality of jade.
The structure of jadeite is usually divided by microscope, and the common structures are equigranular metamorphic structure, columnar metamorphic structure, mylonite structure and fiber interwoven structure. High-quality jadeite is a fiber interwoven structure. The fiber interwoven structure is that after the jadeite aggregate is formed, it is subjected to dynamic metamorphism in the later stage, so that the large-particle crystals are broken into fibrous small particles, and there is a certain directional relationship between minerals (pictured).
Fiber interwoven structure of jadeite
Step 4 color
Jade is rich in color and is the most beautiful of all jade. Its basic colors mainly include the following categories:
Emerald of various colors
White, also known as Bai Fei, is a jadeite aggregate without impurities. In nature, it is usually white with light gray, light green or light yellow and brown tones. Bai Fei has a large output, which is mainly used for carving.
Green, the main color of jade, is called "Cui". According to the depth of green, it can be divided into light green, green, dark green and dark green. The green color of jadeite is mainly caused by trace chromium and iron plasma in jadeite. The higher the content of these impurity ions, the deeper the green color. For example, when the chromium ion content in jadeite is appropriate (a few ten thousandths to a few thousandths), the color is emerald green; When the chromium content is high (above 1%), the color is dark green; When Fe3+ is contained, the color is dark green.
Purple, also called violet. According to the color depth, it can be divided into light purple, pink purple, purple and blue purple. Some people think that purple is caused by trace manganese; Others believe that it is caused by electron transfer between Fe2+ and Fe3+.
Yellow and red. These two colors are secondary colors, which are hematite or limonite formed by long-term exposure of primary jadeite to ground weathering and leaching, which makes Fe2+ become Fe3+. These weathered minerals enter the gaps between jadeite particles in the form of fine particles, making jadeite appear yellow or red. Red is called "Fei".
Black. There are two reasons for being black. One is dark green, mainly because of its high iron and chromium content. This jadeite has high refractive index and high density. The other color is dark gray-gray-black, mainly because jadeite contains amphibole, chromite and other dark minerals, and the surface is dirty.
In addition to basic colors, jadeite also has combined colors, that is, two or more colors appear on a piece of jadeite. People also give it auspicious and beautiful names, such as the combination of purple and green is called "Spring Ribbon", the combination of red, green and purple is called "Fu Lu Shou", and the combination of red, green, purple and white is called "Fu Lu Shou Xi".
5. Notes
Gloss refers to the ability of the surface of jewelry and jade to reflect light. Emerald is mainly glass luster with a little oily luster. Gloss is related to structural characteristics. Fine-grained, fine-grained jade mineral with strong luster. Gloss is also related to polishing quality.
6. Transparency
It is called water head in the jade world. Emeralds are usually translucent-opaque. Transparency is a very important attribute that determines the quality of jadeite. Jade with high transparency is crystal clear, which can make the green of jade full, moist, flexible and vivid, giving people a beautiful feeling.
Transparency is related to its structural characteristics. If jadeite is a fiber interwoven structure, the mineral particles are fine, the texture is fine, the transparency is strong and the water head is high. If jadeite is granular or columnar, the mineral particles are coarse, the texture is rough, the transparency is poor and the water head is low.
Transparency of jadeite
7. Difficulties
Because jadeite is an aggregate and contains many impurity minerals, the hardness can be changed. Because the Mohs hardness of sodalite (5.5) is lower than that of jadeite and omphacite (6.5 ~ 7.0), the higher the sodalite content, the lower the hardness. Generally speaking, its hm = 6.5 ~ 7.0, and it is a kind of jade with relatively high hardness.
8. Relative density
The relative density of jadeite is related to mineral species and impurity element content, and its relative density has a certain range. Among the main components of jadeite, the relative density of jadeite is 3.33 ~ 3.40; The relative density of sodalite is 3.40 ~ 3.50, which is higher than jadeite. The relative density of omphacite is 3.34 ~ 3.43, which is slightly higher than that of jadeite. Therefore, the higher the sodalite content, the greater the relative density of jadeite.
The relative density of jadeite is generally 3.24-3.43, which is generally 3.33.
9, refractive index
Refractive index is a stable physical property of gemstones. Different gems have different refractive indices. The kind of gem can be determined by measuring the refractive index.
The refractive index of jadeite is related to its mineral species and impurity element content, and its value can change within a certain range. Among the main minerals of jadeite, the refractive index of jadeite is1.65 ~1.66; The refractive index of sodalite is 1.74, which is higher than jadeite. The refractive index of omphacite is 1.662 ~ 1.723, which is slightly higher than that of jadeite. Therefore, the higher the sodalite content, the higher the refractive index of jadeite.
The value obtained by point measurement method is 1.65 ~ 1.67, usually 1.66.
10, luminous
The phenomenon that minerals can emit light under the irradiation of high energy rays is called luminescence. There are two forms of luminescence: fluorescence and phosphorescence. Minerals emit light under the irradiation of high-energy rays, and when the irradiation of high-energy rays stops, the phenomenon that the light disappears is called fluorescence; If high-energy radiation is stopped, luminescence can exist, which is called phosphorescence.
The luminosity of jadeite is a reference to identify the quality of jadeite. Most natural jadeites have no fluorescence. If the feldspar in white jadeite is kaolinized, it will show weak blue fluorescence. Bleached and glued jadeite can have blue-white fluorescence. Jadeite dyed purple can have orange-red fluorescence.