Opals can be divided into four categories in terms of their body color: white opals, black opals, fire opals and glass opals.
1. ホワイトオパール
The body color of white opal is milky white, and may have some other colors, such as pink and light yellow, but in general it is still white, changing the color to 3-5 色.
2. ブラックオパール
The body color of black opal is blue-black, sometimes dark green, ダークブラウン, and dark gray, which change strongly.
3. ファイアオパール
The body color of fire opal is yellow, red or orange. Some fire opals do not change color. They are called fire opals just like the color-changing varieties.
4. Glass opal
Glass opal is actually white opal with very good transparency. Sometimes it is also classified as a kind of opal, として知られている “Jade Drop Stone”.
Opal can be divided into opal, opal split stone, and synthetic opal according to its origin and processing method.
Opal split stone is a special treatment method of opal. Opal is often produced in the form of flakes. Many opal flakes are of excellent quality, but they are too brittle, so people invented the spelling method. Usually a piece of transparent crystal is covered on the opal. 一方では, it can strengthen the firmness. 一方で, the hardness of the crystal is higher than that of the opal, which improves the durability of the whole gem. Some opals are too thin, and a layer of dark color material is attached to the bottom, sometimes it is black plastic, sometimes it is simply the dark parent rock of the opal. These opal mosaic stones are common in the international market and are accepted by the market, but they must be noted at the time of sale and the price is lower than pure opal gems.
The quality of opal is evaluated in terms of color (body color), color change, clarity and firmness.
1. 色
Body color is best black or dark, white or light color is the second, orange and orange are the second.
2. Change color
The color change should spread all over the opal, even and complete, without colorless “デッドスポット”. The best quality opal should show the seven colors of the spectrum, the more colors appear, より良い, especially the red and rare purple and purple red. The color change should have strong brightness and transparency, and the appearance should be bright, and the more dynamic the better.
3. Cleaness
The less impurities mixed in, より良い.
4. 堅牢性
It is better if there are no obvious cracks. If there is, pay attention to the location and extent of the cracks.