The discovery of opals and the identification of opals and synthetic opals

1.The main distinguishing features of opal.

Opal is distinguished according to the morphology, structure, low RI, low SG and ultraviolet opacity of pigmentation, and the characteristics of pigmentation are the main distinguishing features.

1) The pigmentation has a silky appearance and lengthens in one direction.

2) Pigmentation is irregular flakes.

3) There is a gradual relationship between pigmentation and pigmentation, and the boundary is blurred.

4) Pigmentation has a fibrous or striated structure in one direction.

2.Synthetic opal.

The first synthetic opal was the French company Gilson, and since the 70s of the 20th century, synthetic black opal and white opal have entered the gemstone market. At present, there are more and more types of synthetic opals on the market.

Synthetic opals are similar in appearance and basic physical properties to natural opals. The chemical composition is SiO2·NH2O, but the water content is often less than that of natural opal, and some synthetic products contain a small amount of ZRO, which can have obvious abnormal birefringence, relative density, generally in the following, and the products of different manufacturers vary slightly. Hardness, lower than natural opal.

The main distinguishing feature of synthetic opal is still the pigmentation feature. The most typical features are columnar pigmentation, mosaic pigmentation and well-defined pigmentation boundaries, honeycomb structure.

1) Columnar pigmentation: Synthetic opal has a columnar growth direction, in a specific columnar area, the color of coloration is consistent, if observed in the vertical column direction, it can show columnar color, usually described as "columnar" rising.

2) Mosaic spots: There are clear boundaries between the pigmentation spots of different colors of synthetic opals, which are closely inlaid together to form a "sawtooth" or "harbor bend".

3) Honeycomb structure: The color spots of each color in synthetic opals have honeycomb characteristics, sometimes called "lizard" skin or "snakeskin" structure, which is a typical feature of synthetic opals.

4) Fireworks-like structure: Russian synthetic opal, due to the special process, the SiO2 pellet produces a certain distortion, so that the growth area does not show columnar color spot characteristics. The appearance and structural features listed above are close to natural opals.

However, the radial fireworks provide a basis for the identification of synthetic opals.

Coober Pedy in southern Australia, discovered circa 1915, is mainly a source of white opal.

Brazil's high-quality white opals are abundant in placer mines.

1. Black opal.

Refers to the black or gray body color and has a color change effect of precious opal, is a precious variety in opal. Opal is Australia's national stone and October birthstone. A colored opal that exhibits a bright color on a dark body hue is called a black opal.

Black opals are found in Lightning Ridge, New South Wales, Australia, and are the most well-known and expensive opal variety. Black opal doesn't mean it's completely black.

2. White opal.

A type of opal in Australia, which generally refers to white (colorless) or light body color, transparent to slightly transparent, with color change or special sparkle effect. As long as the rough stone allows, the white opal is processed into a convex waist round shape; When limited by the thickness of the rough stone, it is also processed into a flat waist round type, but such a thin type is fragile.

3. Crystalline opal (can be black opal, white opal).

The body hue is transparent or translucent, and other items behind it can be seen through the crystalline opal. Crystalline opals can have dark and light embryonic body tones, so we call them "crystalline black opals" or "crystalline white opals" depending on the shade of the embryonic body.

4. Fire opal.

Translucent to opaque varieties with no or little color variation, generally orange, orange-red, red, and the vivid red is the most expensive in fire opals.

5. Gravel opal.

Color-revealing opals are attached to iron ore that cannot be separated, and are mainly produced in Queensland, Australia. This opal can only be cut in conjunction with the iron ore, and a thin colored opal is wrapped around the surface of the iron ore.

Opal has congratulatory relatives (stool stools).

a.Dispersion phenomenon.

b.Discoloration effect.

c.Color change effect.

d.Pleochroism.

Correct Answer: c

Here's how to identify a real opal from a fake:

1. In terms of color and distribution, the color of opal stone is bright and soft, but the distribution is uneven, and the center stone can be placed in the water, and pink patches or straight ribbons can be seen. Synthetic opals come in shades and shades, and are generally more uniform, with a gray hue.

2. Inclusions. Opal stones can be seen in tiger cured cracks or empty flocculent gas-liquid inclusions. Opal inclusions are rarely seen, and occasionally only thin plate-like colorless seed crystals or white bread crumbs can be seen.