Quality identification and selection of tourmaline

Quality identification of tourmaline

1, color

Rose red, purple, green and pure blue are the best, pink and yellow are the second, and colorless is the second.

2. Clarity

It is required to have as few internal flaws as possible, and the crystal clear tourmaline is the most expensive. The tourmaline containing many cracks and gas-liquid inclusions is usually used as a jade carving material.

3. Weight

The higher the weight, the higher the price.

4. The cutting work should be regular, the ratio is symmetrical, and the polishing is good. Otherwise it will affect the value.

Like most crystals, tourmaline will have better luster when exposed to popular people, and the crystal will be more transparent. Generally, it will change more obviously in a short period of time, so the newly purchased tourmaline of the same level is not. After a period of wearing, the tourmaline is beautiful.

Tourmaline selection

Everyone in the tourmaline will often see it in the place where crystals are sold, and many people think it is crystal! In fact, it is a gemstone, and it is a fine gem.

Its color is easy to distinguish, mainly depends on the overall clarity and the degree of the body, the good color, very thorough, and especially bright, let you feel a layer of oil!

Purely monochromatic, the Uni-colored is very rare. Most of the crystals have multiple layers of color or even different colors. Usually the colors are layered. Brazil produces a tourmaline with a red inner layer, which is whiter than the inner "skin" and green on the outer ring. South Africa's tourmaline is green and the outer layer is red. A tourmaline is called "water-melontourmaline" if the inner ring is red and the outer ring is green. After the section of the slice is polished, these color and color changes can be clearly observed.

Cat-eye tourmaline is also present in a variety of colors, but only pink and green types have a strong catoyancy due to the inclusion of foreign crystals. Some tourmalines also show slight variations in color under artificial light sources.

After heating and subsequent cooling, or applying pressure, or rubbing with silk or wool when the weather is dry, a tourmaline crystal will become a charged body. In the direction of the vertical C-axis, one end will produce positive static electricity, and the other end will generate negative static electricity, which will attract some dust particles or even small pieces of paper. This is the piezoelectricity of the tourmaline, which is currently used. Measure the pressure generated by air or water explosion. The first Dutch people who introduced tourmaline to Europe already knew about this effect. They used a heat-treated tourmaline to suck out soot from their sepiolite pipes and called it "aschentrekker" (a tool that approximates the soot extraction).

The tourmaline deposits are usually located in the pegmatites and alluvial deposits. The most productive deposits are Brazil except for Sri Lanka and the Republic of Malaga (Madagascar). Brazil produces red, green and blue tourmalines, and recently it discovered a special color of the tourmaline called "Paraiba", its color is different from other gems, green with blue, like lake green, the color is beautiful and special, but Because the output is scarce, the price is very expensive and it is very popular among Japanese people. Mozambique supplies the finest red and two-tone tourmalines. More deposits are located in Angola, Australia, Myanmar (Red Tourmaline), India, Rhodesia (New Bavi), Namibia, Tanzania, Thailand, Russia (especially the Wula and Caucasus mountains) , more purple, red and blue tourmaline) and the United States (California is the most famous red tourmaline, Maine is red, green and watermelon tourmaline, others such as New York, Connecticut, Colorado, etc. also produced tourmaline). As for Europe, collectors discovered tourmalines on Elba Island and Switzerland. In addition, the tourmaline was imported into China during the Qing Dynasty, and it was used as a gemstone for the top of the hat or the second-class official.

The most demanding colors are pink, bright red and green. Red and green tourmalines are the most common and popular, but only medium-dark and vivid colors are the best. If the color is too dark or too light, the value is greatly reduced. . The chrome-green tourmaline is rarer than the red tourmaline and the price is slightly higher. With the color filter test, the chrome-containing tourmaline turns red. Since tourmaline has strong pleochroism, it must be cut. Usually, the cut surface will be parallel to the spindle core C. However, in the case of light-colored tourmaline, in order to obtain a darker color, the cut surface should be perpendicular to the spindle core C. This is because the tourmaline is dark in the direction of the vertical C axis, while the direction parallel to the C axis is light.

When heated to about 842-1202°F/450-650°C, the tourmaline can produce a slight color change: the green tourmaline turns into an emerald green, while the red-brown tourmaline turns into a red fire. In general, there is no synthetic synthetic tourmaline that is commercialized. Due to the rich variety of colors, tourmalines are often confused with other natural gemstones, especially amethyms, andalusite, chrysoberyl, citrine, demantoid, emerald green. Hiddenite, peridot, smokyquartz, ruby, emerald, synthetic green spinel, peachtopaz, fushan (idocrase), zircon (zircon) and some glass imitations. The important identification of tourmaline is the relatively high double refractive index (doublerefraction) and strong pleochroism. Red tourmaline and opal are the birthday stones of October.