Yu Du
Duyu was called dushan jade in ancient times, and its mining area is located in Dushan, Nanyang County, Henan Province, hence the name.
Nanyang jade is plagioclase jade with fine and pure texture, oily or glassy luster, good polishing performance, and transparent or slightly transparent. The hardness is 5.5 to 6.5 degrees. Nanyang jade is a colorful jade. Generally, multicolored jade composed of two or more colors is brightly colored, which is called: water white jade, white jade, black and white jade, green jade, green white jade, azure jade, jadeite jade, purple jade, bright brown jade, topaz, topaz, jet jade and variegated jade. Nanyang jade mining has a long history. The Neolithic Longshan culture unearthed in Shenmu, Shaanxi Province, the Yin Ruins jade unearthed in 1952, and the jade unearthed in 1976, all have examples of Nanyang jade as jade materials. The jade pots of the Yuan Dynasty now displayed in Beihai and Yuanmingyuan are also made of Nanyang jade carvings. According to the literature, Nanyang jade was exploited in the Han Dynasty. There are more than 1000 ancient jade mining pits in Dushan so far, which shows that Nanyang jade mining has a long history and a huge scale.
Performance of basic physical properties of Duyu:
1, chemical composition: mainly composed of silicate minerals, with complex components (SIO243.83, Al2O31.55, CaO 19. 1 1, others are Cr, Ti, Fe, M n and M g. ).
Crystallization characteristics: It is composed of a variety of minerals (plagioclase, zoisite, tremolite, actinolite, epidote, chlorite, diopside, chromite mica and biotite), with interwoven granular structure, and is a dense massive aggregate. This rock is called altered plagioclase.
3. Hardness: 6-6.5.
4. toughness: strong.
5. cleavage: no.
6. Fracture: granular and hackly fracture.
7, color: changeable.
8. Transparency: translucent and opaque.
9, luster: grease luster.
10, texture: delicate.
1 1, specific gravity: 2. 70-3.0 1, averaging about 2. 90.
12, refractive index: due to the complex mineral composition, it is not displayed on the refractive index meter.
13, special inclusion: none.
14, reaction under the color filter: the green with blue taste of water turns red, while the yellow taste on the dry ground remains unchanged.
15, heat and acid-base: little effect.
Dushan jade is characterized by rich colors, different shades and uneven distribution. Because of different mineral combinations, the same piece of jade often has multiple colors, which is consistent with the technical classification standard. Gemmological classification is also marked by color. dushan jade is divided into the following eight varieties:
(1) white jade: generally white, milky white, often translucent to slightly transparent or opaque. According to the different transparency and texture, there are three names: translucent white, oily white and dry white, among which translucent white is the best, and white jade accounts for about 10% of the whole dushan jade.
(2) Red Duyu: It is often pink or hibiscus, with different shades, generally slightly transparent to opaque, and has a transitional relationship with white Duyu. The content of this jade is less than 5%.
(3) Emerald: including green, gray-green, blue-green, yellow-green, often accompanied by white jade, with uneven color distribution, mostly in irregular bands, filaments or blocks. Transparency varies from translucent to opaque, among which translucent blue-green jadeite is the best variety in dushan jade, and some people call it "Tianlan Jade" or "Nanyang Jade" in business. In recent years, the yield of this high-quality variety is decreasing. But it is mostly gray-green opaque green jade.
(4) Yellow poisonous fish: it is yellow or brownish yellow in different shades, often translucent, often with white or brownish yellow lumps, which is a transitional color.
(5) Brown jade: dark brown, taupe, yellowish brown, with different shades. This kind of jade is often translucent, and it is often in a transitional state between gray-blue and green jade.
(6) Emerald: cyan, gray-cyan, blue-cyan, often in the form of blocks, bands and opacity, which is a common variety in dushan jade.
(7) Black sole jade: Also known as "jet jade", it is black, dark green, opaque, with coarse particles, often in block, block or dot shape, accompanied by white sole jade, which is the worst variety in dushan jade.
(8) Variegated jade: Two or more of the above colors are often displayed on the same specimen or finished product, especially on some large dushan jade raw materials or sculptures, four to five or more color varieties often appear, such as cyan, white, brown, cyan, ink and other colors are disseminated or gradually transited on the same piece, and even on the torus less than 65,438+0 cm, brown and green will appear. Variegated jade is the most common variety in dushan jade, accounting for more than 50% of the total reserves.
In the above classification, except for green and variegated jade, the main color distribution area of other varieties should account for more than 90% of the whole block. As far as jadeite is concerned, the green part is immersed in white jade alone. When the area of the green part exceeds 20 ~ 30%, it can be called jadeite alone. In addition, two or more colors are called variegated jade.
Identification of Duyu: Similar to most jadeites, the quality evaluation of dushan jade is still based on color, transparency, texture and blockiness, and the raw materials are divided into five grades: super grade, first grade, second grade, third grade and so on. High-quality dushan jade requires dense, delicate, crack-free, white-ribbed, impurity-free, single and uniform color, and emerald green is the best. Translucency and near transparency are top grades, and the bigger the block, the better.