Dushan jade, dushan jade - Education and Training Encyclopedia

Dushan jade, dushan jade

I. Overview

Dushan jade is named after its mining area is located in Dushan, which is about 200 meters above the ground in Nanyang Basin, about 0/8 km north of Nanyang. It is a unique jade mineral in China.

Dushan jade is a mineral aggregate mainly composed of plagioclase, plagioclase zoisite and other minerals that have reached the jade level in the geological process.

The first definition emphasizes that dushan jade is formed by geological processes, that is to say, it is naturally formed; Secondly, it is emphasized that it is an aggregate mainly composed of plagioclase and plagioclase zoisite, which is different from plagioclase and other jade.

China has a long history of developing and utilizing dushan jade. For example, a jade shovel made in dushan jade about five or six thousand years ago was unearthed at the Neolithic cultural site in Huangshan, Nanyang County. Shagangdian Village at the foot of Dushan Mountain is said to be called "Yujie Temple" in the Han Dynasty, which was the former site of jade processing in the Western Han Dynasty more than 2,000 years ago.

Domestic authors have studied dushan jade from the perspectives of ore deposit science (,199 1), mineralogy (,1987) and jade science (,200 1).

Second, the mineral composition and chemical composition

(1) mineral composition

There are many constituent minerals in dushan jade. The main minerals are plagioclase (20% ~ 90%) and plagioclase zoisite (5% ~ 70%). Followed by chromium-containing muscovite (5% ~ 15%), diopside (1% ~ 5%), amphibole, biotite, sphene, rutile, epidote and actinolite.

(2) Mineral chemistry

Now, the author and Jiang Nan (master thesis, 1993) will briefly describe the research results of mineral composition in dushan jade as follows.

1. plagioclase

Plagioclase is a homogeneous isomorphic series of NaAl[Si3O8]-Ca[Al2Si2O8]. Anx is generally used to represent the molecular percentage of end members of calcium-bearing feldspar in plagioclase, that is, plagioclase brand, which is called albite, anorthite, intermediate feldspar, Labrador, bytownite and anorthite with 10, 30, 50, 70 and 90 as boundaries. Plagioclase is the main component mineral of permeable white jade, green jade and purple jade, and its content is above 80%. Dushan jade content of other varieties is second only to plagioclase zoisite, which is the most important jade-forming mineral in dushan jade. See table 19-5- 1 for the analysis data and calculated values of plagioclase in dushan jade.

Table 19-5- 1 dushan jade plagioclase electron probe analysis data (wB/%)

As can be seen from the table, except for the dry white dushan jade an = 43.4 ~ 58.3, all others are anorthite, with an = 90.2 ~ 99.2.

2. epidote minerals

The plagioclase zoisite ca 2 Al 2[si2o 7][SiO 4]O(OH) and epidote ca2feaal2 [si2o7] [sio4] o (oh (oh) are completely isomorphic series, and the Al in the chemical composition of plagioclase zoisite can be replaced by Fe3+, if Fe3+< 0.33 ~ 0.45 is plagioclase zoisite (orthophoto). If Fe3+> 0.33 ~ 0.45 is epidote (negative light) (wang pu et al., 1984). According to the data in table 19-5-2, probe analysis, X-ray powder crystal analysis and research under polarizer (master's thesis by Jiang Nan, 1993), the minerals of the epidote group in dushan jade are mainly plagioclase zoisite, a little epidote and zoisite. Oblique zoisite is the main component mineral of dry white jade, pink jade, green and white dushan jade and miscellaneous dushan jade, and its content is more than 60%. Epidote is the main chromogenic mineral in khaki dushan jade. Zoisite only appears in the transparent white dushan jade. The results of probe analysis of this group of minerals are shown in table 19-5-2.

Table 19-5-2 Analysis Data of Oblique zoisite and zoisite Probes

3. mica

According to probe analysis, X-ray powder analysis and polarizing microscope study, mica minerals in dushan jade are mainly distributed in green dushan jade and purple dushan jade, including muscovite, chromic muscovite, chromic nacreous mica and chromic biotite.

(3) Chemical constituents of dushan jade.

Table 19-5-3 Chemical Analysis Data of dushan jade

Our chemical analysis of jade (1-4) and the chemical analysis data (5-8) collected from Henan Geological Survey Team 4 and Henan Geological Survey Team 19 are listed in Table 19-5-3. As can be seen from the table, all jade varieties are poor in silicon, iron, magnesium, potassium and sodium, and rich in calcium and aluminum. Due to the different mineral combinations of different varieties, the chemical composition is also different, ranging from: SiO 2 40.1.8% ~ 44.35%; al2o 3 22.35% ~ 34.42%； cr2o 30.04% ~ 0.34%； fe2o 30. 10% ~ 0.6 1%； CaO 17. 12%~24.02%，Na2O 0.04%~ 1.55%，MgO 0. 19%~2.93%，FeO 0.37%~0.73%，K2O 0.03%~ 1. 15%。

Third, physical properties.

1. color

There are white, green, purple, turquoise, yellow and black.

2. Other physical attributes

Glass luster, density 2.70 ~ 3.09g/cm3, hardness 6 ~ 7. Optical properties are heterogeneous aggregates. The refractive index is 1.560 ~ 1.700. Ultraviolet fluorescence is blue-white, brownish yellow and brownish red. Compressive strength 16.8kg/mm2, tensile strength10.58kg/mm2, shear strength 5.2kg/cm2, fire resistance 1592℃, translucent ~ slightly transparent, fine and compact structure.

Fourth, the types of dushan jade

There are many kinds of dushan jade, which are mainly divided into the following varieties according to their colors:

1. Transparent white dushan jade.

Light gray, the main minerals are anorthite 80% ~ 90%, plagioclase zoisite 10%, diopside 5%, the granularity of columnar granular structure minerals is 0.05mm×0.06mm, oblique zoisite is 0.04mm×0.2mm, diopside is 0.0 1 mm× 0.065438+.

2. Dry white dushan jade

Milky white. Major minerals: feldspar and Labrador 20% ~ 55%, plagioclase and zoisite 45% ~ 80%, and minor minerals are sphene, tourmaline and potash feldspar. Granular structure, columnar structure. The mineral granularity of plagioclase is 0.04 mm× 0.04 mm, and the plagioclase zoisite is 0.03 mm× 0.14 mm. ..

3. Green and white dushan jade

Green and white. Main minerals: anorthite 60%-80%, tremolite15%-20%, diopside10%-20%, plagioclase zoisite10%-0/5%. Secondary minerals include epidote and sphene. The structure is columnar, granular and variegated. The mineral granularity is: anorthite 0.02~0.05mm, tremolite 0.02 ~ 0.0 1 mm, diopside 0.03mm×0.04mm, plagioclase 0.08 mm× 0. 12 mm, which can be subdivided into uniform green and white: mottled green and white according to the green form.

4. Huang dushan jade

Light yellow to khaki. Major minerals: anorthite 30%, epidote 30%, plagioclase 40%, and minor minerals include actinolite and sphene. , with anisotropic and columnar crystal structures. Particle size 0.02 ~ 0. 1 mm

5. Purple dushan jade

The main minerals are anorthite, 85% ~ 90%, Labrador, 5% ~ 10%, zoisite, biotite, epidote, 1%, a small amount of actinolite, inlaid with granular structure, and the granularity of columnar granular structure is 0.0 1 ~.

6. Green dushan jade

Emerald to dark green, the main minerals are about 90% anorthite, about 10% chrome muscovite, and the secondary minerals are biotite and epidote. Granular structure, scaly granular structure, particle size of 0.02 ~ 0.05 mm.

7. Green dushan jade

The main minerals are clinopyroxene 10%, anorthite 80%, Labrador 5% and secondary mineral diopside 5%. Zoisite has a columnar granular structure, and the particle size is 0.03 ~ 0.05 mm for plagioclase and 0.05 ~ 0.5 mm for diopside.

8. Za dushan jade

Dushan jade with more than two main colors is called Za dushan jade, which is the main variety of dushan jade and constitutes the main body of dushan jade. Emerald has a banded, variegated, disseminated and veined structure.

9. Black dushan jade

Dark green-dark green, semi-amphibian mylonite gabbro is the lowest grade jade in dushan jade.

Verb (abbreviation of verb) The difference between dushan jade and similar jade.

The colors in dushan jade are bright and complicated. Generally, there are many colors on the same piece of jade, such as white, green, brown and dark green. This feature is not available in other middle and low-grade jade materials. Dushan jade has fine particle structure and good transparency, which is easy to be distinguished from fibrous jadeite and nephrite.

Six, the basis of economic evaluation

Dushan jade is divided into four grades according to the uniformity of color, texture and blockiness.

Super grade, single green or blue-white, green-white, fine texture, no white ribs, no cracks, and the number of blocks is more than 20kg.

Grade I: white, milky white or green, with bright color, no cracks and impurities, and the weight of the block is above 5kg.

Grade II: dry white, green or variegated, with bright color, no cracks and impurities, and the block weight is above 3kg.

Grade III: bright color, slightly cracked, slightly impurity, and the block weight is above 1kg. The variegated block weighs more than 2 Jin. Dushan jade is a mid-range jade material, and the price varies greatly. The average premium product is seven times that of the third grade product.

Seven, dushan jade deposit industrial genetic types.

Dushan jade is located in Dushan rock mass in the suburb of Nanyang, Henan, China. The exposed part of rock mass is oval, and the strike is NNW-SSE. It is 2.6km long, 0.6 ~ 1 km wide and covers an area of about 2.3km2. Both sides of the rock mass are controlled by faults F 1 and F2. According to the dynamic metamorphism, the rock mass can be divided into gabbro zone, mylonite gabbro zone and gabbro fracture zone. Jade vein occurs in the middle and upper part of gabbro fracture zone in the middle of Dushan, and its strike is the same as Dushan rock mass (330). The jade vein dense zone is > >1200m long and 60 ~150m wide, and the jade vein ore body strikes 55 ~ 95, 165438. Jade veins with dip angle of 55 ~ 70 are generally distributed in the shallow part of gabbro body. In the wild, obviously, jade veins invaded in multiple phases. Medium-grained plagioclase first invaded gabbro fractures and occupied gabbro, and jade veins formed later. The first jade-forming period is the formation period of multi-color jade veins, starting from penetrating white jade → dry white jade → green jade → green white jade → purple jade → azure jade; The second phase became jade, and it was dry white jade. From the vein wall to the center, the distribution law of jade appears from shallow to thick and then to shallow. The shape of jade veins is complex and diverse, with veins as the main form (70%), followed by lenses (20%). It is often distributed along intermediate tension cracks or fault zones in pyroxene and plagioclase, with filling as the main factor and metasomatism as the auxiliary factor. The boundary with surrounding rock is clear, forming single vein, tree root, staggered network vein, block, symmetrical strip, parallel strip and metasomatic residual structure. This frequent occurrence of veins shows the characteristics of hydrothermal mineralization. The research shows that dushan jade is a high-temperature hydrothermal deposit after plagioclase magmatism, and its formation temperature is 355 ~ 430℃. Jade is the product of many stages. With the hydrothermal solution from early to late, Ca, Cr, Fe and Ti ions gradually increased, and the color of jade changed from colorless to white to green to purple to sky blue. The grade of plagioclase is from An97→An98→An 100, and the second phase white jade appears after pigment ion precipitation.

Think about a problem

First of all, is it right or wrong?

1. Green jadeite is mainly colored by biotite minerals.

2. The color of green jadeite is mainly caused by muscovite minerals.

3. The color of green jadeite is mainly caused by muscovite minerals containing chromium.

Second, multiple choice questions

1. The color of purple jade is determined by: ()

A. epidote

B. diopside-containing

C. chrome biotite

2. The main mineral composition of dushan jade is: ()

A. diopside and amphibole