Hardness 6 specific gravity 2.00-2.10
Refractive index 1.40-1.46
Wear: very soft, avoid high temperature, dry and strong light
Opal is an amorphous gem, which can be divided into two varieties: one has play of color, which is called precious opal; the other has no change of color, which is called common opal.
The main components of opal are silica and water (SiO2 · nH2O), also known as opal, opal and cloud.
Opal is an October Birthstone.
Human understanding of opal
In the Roman era around 250 B.C., "opal" was once regarded as the highest gem. Its name may come from the Sanskrit "Upala", which means "TOP GEM". This is because people don't know the reason why opal emits rainbow like color light. It is believed that opal is a gem that gathers small particles of ruby, sapphire, green gem and other colors together.
In the middle ages, people thought "opal" could bring good luck, because "opal" gathered all the colors of gemstones.
In 1829, Scottish novelist Sir Walter Scott described an opal with supernatural power in the novel Anne of geierstein. In the novel, the opal amulet belonging to the Baroness can show the color of the master's mood. When a drop of holy water drops on the amulet, the opal becomes a colorless stone, and the Baroness dies soon.
The novel was once very popular in Europe. One year after its publication, the sales volume of "opal" in Europe fell by 50%, which led people to associate "opal" with bad luck. This influence continued even into the 20th century.
According to the legend of Aboriginal people in Australia, when the creator came to the earth with a rainbow, "opal" was born. When his feet touched the ground, the gems around him began to shine, showing all kinds of colors of the rainbow.
The reason why "opal" became colorful
The color change of guiopo is caused by the phenomenon of diffraction of light. Guiopo is composed of tiny spheres of silica arranged in regular order. When light passes through the sphere of silica, it will refract and emit a rainbow like spectrum.
As long as you change the observation direction of guiopo, you can enjoy the flexible rainbow color, which is play of color. The final effect of color changing depends on the size and arrangement of silica spheres.
The description of "black opal" or "White Opal" refers to the color of the background showing the color change. Generally speaking, the darker the background, the brighter the color change and the higher the value.
The formation and origin of "opal"
Silica with low temperature (about 50 ℃) and water content is deposited in cavities and fractures of rocks, forming "opal". It is also possible for the "OPA" to penetrate into the animal and plant tissues or fossils in the stratum and form the fossil "OPA".
From the Roman era until the discovery of the Australian mining area in the late 19th century, the "opal" has been mined near czerwenitza, Slovakia. In 1872, "opal" was first discovered by Listowel downs in Central Queensland, Australia.
At present, the main producing areas of "opal" are Australia and Mexico. Australia produces "White Opal" and "black opal". Mexico produces "Water Opal" and "Fire Opal". Ethiopia is also an important producing country of "opal".
Factors affecting value
The quality level of "opal" is determined by various elements including background color and color changing effect. The price of black opal is higher than that of white opal, and the value of vivid opal is higher. Red is the most popular color among the variable color.
The price of opal made in Australia is much higher than that of opal made in Mexico, because opal made in Australia has better stability, while opal made in Mexico will dehydrate when exposed to the air for a long time.
Wearing and preservation
Opal is a very fragile gem with a hardness of only 6, which is softer than the dust in the air. It can only be wiped with a wet cloth or a dry cloth to avoid abrasion, heating, drying and high temperature storage environment. It should be stored together with a wet cotton ball or a dish of distilled water as far as possible to avoid cracking or cracking due to dehydration.
Avoid direct sunlight or other strong light. Avoid any chemical or detergent contact, including perfume and hair spray. Avoid ultrasonic cleaner and steam cleaner. Do not wear "opal" jewellery for shower.