Opal
Opals – natural stones
Opals are considered the most precious and valuable stones. They possess a beautiful play of colors and are characterized by a variety of colors. Opals are divided into:
- Precious opals – exhibiting opalescence, the play of colors.
- Common opals – exhibiting opalescence.
Opal is a hydrated form of silica. It contains between 3% to 20% water, and its hardness ranges from 5.5 to 6.5 on the Mohs scale. Opal stones should not be classified as minerals but as mineraloids because they lack a crystalline structure. They are composed of small spheres called spherolites, which, due to their close packing and formation into regular blocks, cause the occurrence of a play of light. Opals often contain inclusions of other minerals, such as moss opal, as well as liquid and gas inclusions.
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Origin and Formation of Opal
Opals are formed through weathering, metasomatic, and hydrothermal processes. Water flowing over the earth collects silica from sandstone into voids and cracks, which are formed due to natural faults or decomposing fossils. Then, as a result of evaporation, silica sediment forms. This cycle must repeat many times for opal to form as the final result. This stone is a component of sedimentary rocks and occurs in geyser deposits, hot springs, and igneous rocks. Sometimes, it can also be observed in the remains of animals and plants, known as fossilized wood. Currently, opal is the national gemstone of Australia, and this country is its largest producer. In addition, opals used in jewelry mainly come from Slovakia, Ethiopia, Mexico, Peru, Brazil, and Honduras.
Opals and Their Varieties in Our Online Store
In our online store, you will find both faceted opal stones and cabochons. Opal stones have many varieties, but precious opals are the most popular in jewelry. We offer the following types of opals:
You can find opals in shapes such as cushion, marquise, hexagon, trillion, pear, irregular, oval, and round. Opals have many varieties, but precious opals are the most popular in jewelry.
Appearance of Opals: Colors, Types, and Visual Effects
The effects observed in opals are opalescence and play of color. Precious opals exhibit the phenomenon of opalescence. The play of colors involves the refraction, diffraction, and reflection of light on silica globules inside the stone. However, these globules must be densely packed to produce an intense effect. The color of the light flashes and their appearance depends on the sizes and differences in size of the silica globules. Opalescence, on the other hand, occurs in common opals and involves the scattering of light upon contact with matter, resulting in a glow from the scattering center. In this case, you can observe a blue, blue-white, or milky-white glow. Opals can also sometimes exhibit asterism and cat’s eye effects. We distinguish 7 main types of opals based on the main color of the opalescence effect:
- Milky (lechosos) – these are precious opals with a dominant white to slightly gray play of color.
- Blue– refers to stones with a dominant blue or purple opalescent effect.
- Fiery – the name refers to opals with a red play of colors.
- Peacock – the name refers to the peacock’s plumage, indicating stones with an opalescent effect that is a combination of blue, green, and purple colors.
- Green – the name refers to precious opals with a dominant green color of the opalescent effect.
- Golden – these are precious opals with a dominant opalescent effect ranging from yellow to orange or opals with a yellow inherent color.
- Pink – this is one of the most expensive and sought-after varieties of opal, with a dominant pink color of the opalescent effect.