Opal Gemstone
Opal is naturally found in a white coloured semi-precious gemstone composed of a silicate mineral family recognized for its marvellous ‘play of colours’. This astrological alternative of precious diamond is worn for gaining success in innovative pursuits, lavish lifestyle, social/financial prominence, matrimonial harmony and good health. Over thousands of years, people have quarried and treasured opals. These striking opal stones have energized a rich body of folklore. (Thus, opal gemstones have been considered both the luckiest and unluckiest stones one can wear).
[Image will be uploaded soon]
Factual Information About Opal Gemstone
Assembled Opal Gems
A triplet from assembled opal gems adds a transparent quartz cap and makes for a good opal stone ring and opal earrings, since the hard quartz keeps the softer opal from scratching.
How to Determine Synthetic Opals?
Synthetic or lab-created opals are actually the real opals, but they’re grown in laboratories rather than yellowish-brown underground. They encounter the same formation processes, only at a stimulated rate in controlled settings.
Synthetic opals may exhibit an intense display of colour, generally in a mosaic pattern. With high magnification and backlighting, you can find a scale-like, snake skin or chicken wire structure in the pattern. When put under high magnification with transmitted light, synthetics may display a dendritic structure. Synthetic opals don’t phosphoresce (sparkle or twinkle) and may also stick to the tongue.
How to Detect Fake or Imitation Opal Gems?
Contrary to lab-created opals, imitations only simulate the physical look of opals. These imitations are essentially made from glass or plastic.
Plastic imitations or stimulants are soft and can be dissected with a sharp needle. They do not sparkle or twinkle (phosphoresce).
Glass stimulants essentially consist of glass bubbles and swirl marks. They also do not phosphoresce. Their refractive index (RI) and specific gravity (SG) are also generally higher than natural opal.
Care For Opal Stones
Nowadays, used frequently as opal necklace, opal rings and other opal jewellery, extra care of the delicate gemstone is well worth it. Highly sensitive to changes in temperature as well as a “crazing”, that implies they can easily form cracks or “craze” as they dehydrate, and must be kept cautiously.
Opals kept in water must be dried properly and cautiously before cutting.
Sometimes opals in rings can become chalky white and weary. This may owe to a network of scratches on the opal surface that dismantle the polish and dulls the colour play. However, a simple re-polishing can generally correct this. Having a hardness of only 5.5 makes them quite susceptible to scratching. Opals are thus usually not recommended for ring stones, unless the stone is positioned in a protective setting or a triplet for occasional wear.
Opal Stone Facts and Information
Opal stone is sedimentary.
Many ancient references to opal may actually indicate other gems, such as the iridescent iris agate.
Under proper conditions, water seeps through the earth, becoming affluent in dissolved silicates. When water makes way through a cavity, it accumulates the silicates as microscopic spheres, forming opals.
FAQs on Opal
1. What is an opal from a geological perspective?
Geologically, opal is a hydrated amorphous form of silica (SiO₂·nH₂O). Unlike crystalline minerals like quartz, opal does not have a rigid crystal structure, which is why it is classified as a mineraloid. Its water content is variable, typically ranging from 3% to 21% by weight. It is most commonly found in the fissures of rocks such as limonite, sandstone, and basalt.
2. How can you differentiate between a precious opal and a common opal?
The key difference lies in their internal structure and appearance.
- Precious Opal: Exhibits a unique optical effect known as 'play-of-colour'. This is caused by light diffracting off microscopic, uniformly sized and arranged silica spheres.
- Common Opal: Lacks a play-of-colour because its internal silica spheres are of random sizes and arrangements. It is often opaque, has a waxy lustre, and is valued for its body colour rather than optical effects.
3. What scientifically causes the 'play-of-colour' phenomenon in precious opals?
The play-of-colour is not due to iridescence but is a result of diffraction. A precious opal is composed of countless microscopic silica spheres arranged in a highly ordered, three-dimensional grid. As white light passes through this structure, it is split into its spectral colours, similar to how a prism works. The specific colours seen depend on the size of the spheres and the angle of observation.
4. What are the main geological and commercial uses of opal?
Opal's uses are primarily determined by its type and quality.
- Gemological Use: Precious opal is highly valued as a gemstone and is used extensively in jewellery, including rings, pendants, and earrings. Its value is determined by its body tone, brilliance, pattern, and the vibrancy of its play-of-colour.
- Industrial Use: Common opal, while not typically used in jewellery, can be used as a source of high-purity silica in some industrial applications. Diatomite, a type of common opal, is used to make abrasives, filters, and fillers.
5. What geological factors determine the quality and value of an opal gemstone?
Several geological and physical factors determine an opal's value:
- Body Tone: Black opals are generally the most valuable because the dark background provides a stark contrast that enhances the play-of-colour.
- Play-of-Colour: The intensity, range of colours, and pattern of the flashes significantly impact its worth.
- Clarity and Transparency: The degree to which the opal is transparent or opaque affects its appearance and type.
- Origin: Certain locations, like Australia, are renowned for producing high-quality opals, which can add to their value.
6. Why is opal classified as a mineraloid and not a true mineral like quartz?
The distinction comes down to crystalline structure. A true mineral, by definition, must have a definite, orderly, repeating crystalline structure. Quartz, for example, has a fixed hexagonal crystal system. Opal, on the other hand, is amorphous, meaning its atoms are not arranged in a regular, repeating pattern. This lack of a crystalline structure is why it is classified as a mineraloid, not a mineral.
7. How does the significant water content in opals affect their physical stability?
The water (H₂O) within opal's silica structure is integral to its composition but also introduces a vulnerability. If an opal is exposed to rapid changes in temperature, direct heat, or very low humidity, it can lose its internal water. This dehydration can cause the opal to become brittle and develop a network of fine cracks, a phenomenon known as 'crazing'. This makes opals more delicate and require more careful handling than non-hydrated gemstones like diamonds or sapphires.
8. What is the difference between an opal's 'play-of-colour' and gemstone 'fire'?
While both terms describe flashes of colour, their optical causes are different.
- Play-of-Colour: This is caused by diffraction and is unique to opals. It results from light being split by the stone's internal structure of silica spheres.
- Fire: This is the common term for dispersion, an optical property seen in many gemstones like diamonds. It occurs when light passes through the gemstone's facets and is split into spectral colours, much like a prism, but does not rely on an internal grid structure.
