Water opal is a distinctive variety of precious opal, known for its exceptional clarity, often resembling clear water. This transparency allows for a vibrant display of internal flashes of color, known as play-of-color. Unlike opaque opals, its translucence provides a unique window into its captivating optical phenomena.
Unique Characteristics
A primary feature of water opal is its transparency, ranging from translucent to completely clear, often resembling a droplet of water. Its clarity allows light to penetrate deeply, revealing play-of-color—an iridescent shimmer displaying a spectrum of hues that appear to dance across the stone’s surface. The vividness and range of colors, from blues and greens to reds and oranges, are directly influenced by the size and uniform arrangement of the internal silica spheres.
Water opal, like all opals, is composed of hydrated amorphous silica (SiO₂·nH₂O), primarily silicon dioxide with water molecules integrated into its non-crystalline structure. The water content ranges from 3% to 21% by weight, often between 6% and 10%. Its internal structure consists of microscopic silica spheres (150-400 nm in diameter) arranged in a structured pattern, through which light diffracts to create the visible play-of-color. The less silica gel present between these spheres, the greater the opal’s transparency.
Formation and Origins
The formation of water opal, like other precious opals, is a geological process spanning millions of years. It begins when silica-rich water seeps into cracks and voids within various rock types, such as sandstone or rhyolite. As the water gradually evaporates, it leaves behind a deposit of microscopic silica spheres, a cycle that repeats over extended periods, slowly building up layers of silica.
For precious opal to form, these silica spheres must arrange themselves in an orderly, three-dimensional pattern. This precise arrangement allows light to diffract, producing the characteristic play-of-color. If the spheres are randomly arranged, common opal, which lacks iridescence, forms instead. Significant sources of high-quality water opal include Mexico (particularly the Querétaro region), Ethiopia, Australia, and the USA.
Distinguishing Water Opal
Water opal is distinguished from other opal varieties by its unique characteristics. While all opals share a similar composition, their appearance and properties vary significantly. As a precious opal, it exhibits play-of-color, unlike common opal (potch) which lacks iridescence.
The primary differentiator for water opal is its exceptional transparency and stable hydration. While some opals, particularly certain Ethiopian varieties, are hydrophane and can absorb water, true water opal maintains its clarity without such dramatic shifts. Hydrophane opals may become transparent when immersed but can lose their play-of-color or become hazy, reverting as they dry, which can also affect their long-term durability. In contrast, water opal’s inherent transparency is consistent, making its internal colors appear to float within a clear, glass-like medium, and this stable clarity sets it apart from other precious opals.
Care and Preservation
Water opals, like all opals, require careful handling due to their relative softness (5.5-6.5 on the Mohs scale). This makes them susceptible to scratches and impacts, so remove opal jewelry during activities that might cause damage. Opals are also sensitive to sudden temperature changes and extreme dryness, which can lead to cracking or “crazing” as they lose moisture.
To clean water opal, use warm water with a few drops of mild soap and a soft brush or cloth. Harsh chemicals, abrasive cleaners, and ultrasonic or steam cleaners should be avoided, as these can damage the stone or its delicate structure. For storage, keep water opals separate from harder gemstones in a soft pouch or lined jewelry box to prevent scratching. Maintaining some humidity in dry environments, perhaps by placing a damp cloth nearby, can help preserve their internal moisture content.