The terms opal and opalite are frequently confused due to their similar names and visual appeal. Opal is a naturally occurring mineraloid, while the material most commonly marketed as opalite is a manufactured glass product. The term “opalite” is also sometimes used to describe a natural, common opal that lacks the prized optical effect of its precious counterpart.
Genuine Opal: Formation and Composition
Natural opal is a mineraloid, not a true mineral, formed from hydrated amorphous silica, which is silicon dioxide combined with water. This formation process requires silica-rich water to seep into rock crevices and slowly deposit its content over millions of years as the water evaporates. The water content in the resulting material typically ranges from 3% to 21% by weight.
The phenomenon that makes precious opal desirable is called “play-of-color,” a dynamic display of internal spectral hues. This effect is caused by the internal structure, which consists of billions of microscopic silica spheres stacked in a regular, three-dimensional grid. When light enters this ordered arrangement, it diffracts and splits into component colors, producing flashes of red, blue, and green that shift with movement. The size and spacing of these spheres determine which colors are visible, with smaller spheres diffracting blues and greens, and larger spheres producing rarer reds and oranges.
Understanding Opalite: Material and Origin
The material most widely sold as “opalite” is not a stone at all, but rather a man-made glass. This manufactured glass is created using a high-temperature fusion process, often incorporating compounds like dolomite and metal to give it a unique sheen. The resulting material is consistently translucent or milky white, designed to imitate the soft glow of some natural opals.
The name “opalite” is also applied to synthetic opal, a lab-grown material that shares the chemical composition of natural opal and exhibits true play-of-color. However, the most frequent material encountered in mass-market jewelry and decorative objects is the inexpensive, translucent glass. This glass may also be marketed under names like “sea opal” or “opal moonstone.”
Key Visual and Physical Distinctions
Genuine opal exhibits “play-of-color,” where brilliant flashes of multiple, distinct colors move and change across the stone’s surface as it is rotated.
In contrast, the common glass opalite displays a static “opalescence,” which is a milky, soft glow rather than a dynamic spectral fire. This glass material often appears pale blue against a dark background and shifts to a milky white or peach color when held against a light source. Under magnification, glass opalite may reveal tiny air bubbles or swirl marks, artifacts of its manufacturing process not found in natural opal. The hardness also differs: natural opal has a Mohs hardness of 5.5 to 6.5, while glass opalite is typically around 5, making it softer and more susceptible to scratching.
Market Context and Value
The disparity in origin and composition translates directly into a difference in market value. Because opalite is a mass-produced glass, it is inexpensive and widely available. This affordability makes it a popular choice for costume jewelry and decorative items, offering an attractive, luminous appearance at a low price point.
Natural opal, particularly precious opal, is a rare and valued gemstone. Its price is determined by the rarity of its color, the brightness of the play-of-color, and its origin, with high-quality specimens commanding premium prices. While natural opals can range from tens to thousands of dollars per carat, glass opalite holds minimal intrinsic monetary value and is not considered an investment gem.