A star opal pattern is a rare and beautiful phenomenon seen in some opals. It is characterized by a star-like formation of light, usually with four to six rays emanating from a central point. This effect is caused by the diffraction of light within the opal's microstructure, specifically by the regular arrangement of tiny silica spheres.
Star opal is a type of opal that exhibits asterism. Asterism is a phenomenon in which a star-shaped pattern is visible when the stone is viewed from certain angles. The star pattern is caused by the presence of microscopic spheres of silica in the opal. These spheres act like prisms and refract light, creating the star-shaped pattern.
Star opals are typically found in black opals, but they can also be found in other colors. The most valuable star opals are those that have the most distinct and intricate star patterns. Star opals are also known for their ability to change color depending on the angle of view, which adds to their beauty and value.
|Star Pattern Opal. From: Wyoming rush, Wyoming Opal Fields, Lightning Ridge, Finch Co., New South Wales, Australia. Image credit: Cody opal
How Star Opal Pattern forms
This unique pattern arises from the way light interacts with the microscopic structure of the opal. The opal is composed of tiny silica spheres arranged in a regular, ordered lattice. When light strikes these spheres, it diffracts, meaning it bends and separates into its component wavelengths (colors). If the spheres are arranged just right, the diffracted light converges to form a pinpoint of intense color, typically appearing as a six-rayed star.
Rarity and value
Star pattern opals are exceptionally rare, making them highly sought-after by collectors and gem enthusiasts. Their value depends on various factors, including the size, clarity, intensity of the star pattern, and the overall play-of-color. A high-quality star pattern opal can fetch tens of thousands of dollars or even more.
Where are they found?
While rare, star pattern opals have been discovered in several locations worldwide, including:
Lightning Ridge, Australia: Considered the primary source of these opals, known for their vibrant colors and distinct star patterns.
Ethiopia: Known for producing black opals with a distinctive "fire" pattern, sometimes accompanied by a star effect.
Oregon, USA: Home to "Oregon Sunstones," a type of opal that can exhibit a star pattern.