Opal and opalite are materials frequently encountered in jewelry and decorative items, yet they possess fundamental differences. Despite their similar names, they are distinct in origin, composition, and optical characteristics. Understanding these distinctions is important for anyone interested in gemstones, and this article aims to clarify them.
The Natural Beauty of Opal
Natural opal is a mineraloid composed of hydrated amorphous silica (SiO2·nH2O), typically containing between 6% and 10% water by weight. It forms over millions of years as silica-rich water seeps into cracks and voids within various rocks. As the water slowly evaporates, it leaves behind a deposit of silica spheres that gradually solidify into opal.
The defining characteristic of precious natural opal is its captivating optical phenomenon known as “play-of-color.” This occurs due to the precise, orderly arrangement of microscopic silica spheres within the opal’s internal structure. When white light enters the opal, these spheres diffract it, splitting it into spectral colors and creating flashes of vibrant hues that shift with viewing angle. Not all natural opal exhibits this effect; common opal, for instance, lacks the ordered silica structure necessary for play-of-color and usually appears translucent or milky without iridescence.
Unveiling Opalite
The term “opalite” can refer to two distinct materials. In a natural context, it is sometimes used as a synonym for common opal, a naturally occurring hydrated silica lacking the “play-of-color” seen in precious opal. This natural form often appears milky or translucent and can be found in various colors.
However, the more prevalent material sold as “opalite” is a man-made glass product. This synthetic glass is primarily composed of silicon dioxide, often with added minerals like dolomite and metal oxides to achieve its characteristic appearance. It is manufactured by melting these raw materials, creating a material designed to imitate the visual appeal of natural opal. The optical effect of this glass opalite is typically a milky, opalescent glow or adularescence, which differs significantly from the play-of-color in natural opal. This glow often appears blue when viewed against a dark background and shifts to orange or yellowish when placed against a light background.
Core Differences: Opal vs. Opalite
The fundamental distinction between natural opal and synthetic opalite lies in their origin and composition. Natural opal forms geologically over millions of years from hydrated amorphous silica and water, creating a unique internal structure of silica spheres. In contrast, the common form of opalite is a man-made glass, synthetically produced from silicon dioxide and other compounds.
Their optical effects also differ significantly. Natural precious opal displays “play-of-color,” a vibrant internal flash of spectral hues caused by light diffracting through its ordered silica spheres. Synthetic opalite, on the other hand, exhibits a milky, opalescent sheen or adularescence, where light is scattered within the glass, resulting in a consistent glow that changes color based on the background. Natural opals often show irregular patterns and can have natural inclusions, while glass opalite may present a uniform appearance and can sometimes contain small, uniform air bubbles from its manufacturing process.
Natural opal typically rates between 5.5 and 6.5 on the Mohs scale, making it relatively soft for a gemstone. Synthetic glass opalite generally has a similar or slightly softer hardness, ranging from 5 to 6.5 on the Mohs scale, which means both materials require careful handling to prevent scratches. There is also a notable difference in value and cost. Natural precious opals, especially those with vivid play-of-color, are considerably valuable due to their rarity and unique beauty. Synthetic opalite, being a manufactured product, is significantly more affordable and widely available, often used as a cost-effective alternative in jewelry.
Practical Identification Tips
Distinguishing natural opal from synthetic opalite often comes down to careful observation. The most reliable indicator is the optical effect: natural precious opal will exhibit “play-of-color,” where distinct flashes of color appear and shift across its surface. Glass opalite, however, will display a consistent milky or translucent glow, often appearing blue against dark backgrounds and peachy or yellow against light ones, without the dynamic, shifting colors of natural opal.
Another practical tip involves examining the material for internal characteristics. Since synthetic opalite is glass, it may sometimes contain small, perfectly round air bubbles trapped during its manufacturing process. Natural opals, while they can have inclusions, typically do not contain such uniform bubbles. Finally, considering the price can offer a strong hint. If a piece is being sold as opal at a price that seems unusually low for a genuine gemstone, it is likely to be the synthetic glass opalite.