Chinese name
topaz
Foreign name
topaz
subject
Crystallography and mineralogy
quick
navigate by water/air
The origin of the name
distinguish
differentiate
Gem processing
genetic type
Crystal parameters
Composition (wB%): calculated by Al2 [SiO2] (OH) 2, SiO2 33.4, Al2O3 56.6, H2O10.0; ; F can replace OH with a theoretical content of 20.65%. F:OH is 3: 1~ 1: 1, which varies with the formation conditions of topaz: pegmatite type, and the F content is close to the theoretical value. In the greisen type, the content of OH increased to 5 ~ 7%; Hydrothermal type, with similar F and OH contents.
Oblique system, a0=0.465nm, b0=0.880nm, c0 = 0.840nm；; Z=4. The crystal structure consists of O2-, F-, OH-*** and four layers of ABCB, and the stacking layer is ∨( 0 10). Al3 occupies octahedral gaps and forms an octahedral [SiO _ 4] tetrahedron.
Oblique bipyramid, D2h-mmm(3L23PC). Columnar crystal form. Common simplex: rhombic columns M, L, J, rhombic bipyramid N, O, P, Q, parallel double-sided C, B, etc. Cylinders usually have longitudinal stripes. It is usually an irregular granular and massive aggregate. [2]
The origin of the name
Topaz, also known as topaz by mineralogists, is often called topaz in the domestic jewelry industry, which is a transliteration of English. This is mainly because both topaz and topaz will be confused with the original names of some gems in China's jewelry industry. In China, yellow hetian jade (nephrite) has long been called topaz, especially in the field of archaeology; Topaz is easily mixed with topaz in crystal.
Topaz's English name comes from two sources: one is Zebedard Island from the Red Sea, formerly known as Topaz OS, which means "hard to find" and is named after the island is often found in fog; Another saying comes from the Sanskrit TOPUS, which means "fire".
In China's ancient books, topaz is called topaz, Huang Yagu, Huang Hu Ya and Nan Mu, but these words generally refer to all yellow gems, including yellow sapphires and yellow beryls. It is said that topaz recorded in Buddhist scriptures is olivine today. It has the color of Tianhuang and the hardness of jadeite. Compared with nephrite such as Hetian jade, it has better hardness, higher transparency and brighter color. Because it is produced in Longling, the color is mainly yellow, so it is finally named topaz, and some people call it royal jade.
Topaz was only hidden and traded as an ornamental stone before it was developed into jade, and it was called "yellow wax stone". Because of its delicate stone, golden color, huge block shape and rich changes, it has high ornamental value, reaching thousands or even tens of thousands of yuan per kilogram. Its rapid price rise has created a miracle in the history of jade. In fact, not all Huang Yushi can be regarded as topaz. Only Huang Yushi, which has reached the jade level, is called "topaz". [2]
distinguish
Gemstone minerals similar to topaz are tourmaline, topaz, andalusite, apatite and aquamarine.
The specific gravity of tourmaline (3.03-3.25) is less than topaz, which can be distinguished by diiodomethane heavy liquid. Floating on the heavy liquid of diiodomethane, while topaz sinks. Under the magnifying glass, through the watch, you can see that tourmaline is obvious; There is a ghost at the edge of the facet, and topaz has a weak ghost. Tourmaline has obvious dichroism. Except pink and brown topaz is darker than tourmaline, topaz of other colors is lighter than tourmaline, and the two colors are not exactly the same.
The specific gravity of topaz (2.99-3.0 1) is smaller than topaz, which can be distinguished by diiodomethane. Topaz floats on heavy liquid, while topaz sinks in heavy liquid.
Andalusite (specific gravity 3. 17) floats in the heavy liquid of diiodomethane, which is different from topaz. Moreover, andalusite has a strong multicolor, which is much more obvious than topaz.
The specific gravity of apatite (3. 17-3.23) is smaller than topaz, which can be separated by diiodomethane. Apatite is; Uniaxial crystal.
The refractive index (1.566— 1.594) and specific gravity (2.6—2.9) of aquamarine are smaller than topaz. Aquamarine is the axis; Crystal. It is very common for topaz to have cleavage. [3]
differentiate
When the refractive index and specific gravity of glass are similar to topaz, the difference between them is that the glass is isotropic and completely extinction at the cross polarizer. Although there are optical anomalies, it is obviously different from the anisotropic extinction phenomenon of topaz biaxial crystals. Glass has no refraction, is polychromatic and has a single refractive index. Glass contains round bubbles with prominent bubble boundaries, while topaz contains two-phase or three-phase inclusions. [3]
Gem processing
The popular styles of topaz are emerald cut and round cut. In the process of machining, because topaz has cleavage parallel to the bottom surface, attention should be paid to directional cutting to prevent the grinding surface from being parallel to the cleavage surface, which makes it difficult to grind and polish. The reasonable orientation is that the cutting surface and cleavage surface are 12. A 15。 Due to the existence of topaz cleavage, care should be taken when setting the corner to avoid damage. From the color point of view, purple topaz has the highest price, and good quality is expensive. Followed by pink, brown, blue and yellow. Colorless topaz has the lowest price. Topaz often contains gas-liquid inclusions. Clean topaz is rare. Multivalence with inclusion