Black opal 

Black opal is one of the rarest and most valuable varieties of opal, known for its striking play-of-color against a dark body tone. Unlike common opal, black opal has a deep, rich background—ranging from dark gray to jet black—that enhances the vibrant flashes of red, blue, green, yellow, and violet. This phenomenon, known as opalescence, occurs due to the diffraction of light through the microscopic silica spheres that make up the mineral. The most famous and high-quality black opals are found in Lightning Ridge, Australia, which is considered the world's premier source of this gemstone.Black opal is composed of hydrated silica (SiO₂·nH₂O) and has a relatively low hardness of 5.5 to 6.5 on the Mohs scale, making it somewhat delicate and prone to scratching. Unlike transparent gemstones that rely on clarity, black opals are valued for their depth of color, brightness, and pattern. The most sought-after variety is the "Harlequin" pattern, which displays a mosaic of vivid colors in a well-defined arrangement. Other patterns, such as rolling flash, pinfire, and ribbon, also contribute to the gem’s uniqueness. Due to their rarity, high-quality black opals command some of the highest prices in the opal market, sometimes exceeding the value of diamonds. Because opals contain water molecules, they require careful handling to prevent dehydration, which can lead to cracking. Beyond their beauty, black opals hold cultural significance, particularly in Aboriginal Australian folklore, where they are believed to possess mystical and protective properties. Today, they are cherished by gem collectors and jewelry enthusiasts worldwide for their unparalleled beauty and captivating play-of-color.