Opal
Opal is a fascinating and beautiful mineraloid gemstone, a unique combination of oxygen and silica that exhibits a variety of colors and displays an internal play of colors, known as opalescence or fire. Known for its exquisite color play, opal is considered by many as one of the most desirable gems and is a popular choice for engagement rings and other jewelry.
Formation
Opal forms in hosted rocks, usually as a result of the deposition of silica from groundwater, along with other minerals. As sediments build up, water slowly evaporates from them, leaving behind microscopic spheres of silica. These spheres build upon each other, forming distinct layers that form the basis for opal.
Chemistry
Opal is composed of approximately 80% amorphous hydrated silica, and 20% water. Its unique chemical composition and crystal structure cause it to display striking colors and light reflections. This substance found in opal is called silicic acid gel.
Characteristics
Opal is composed of tiny silica spheres that are arranged to form pockets of air. When these air pockets reflect light, the opal displays unique colors, a phenomenon known as opalescence. The opal also displays various colors depending on the angle at which the light is viewed, and how much light it reflects.
Opal has a range of hardness, with some varieties being as hard as quartz, while other varieties may be as soft as a fingernail. Its transparency can range from clear to fully opaque. When subjected to intense pressure, opal can also be permanently damaged or broken.
History
The original source for opal gemstones is not known, however it is believed that the Ancient Greeks and Romans mined opal in the area of the Middle East. During the Roman period, opal was highly prized and was a favorite of Emperors and Kings.
In the Middle Ages, opal was thought to have magical powers, and was often used to foretell the future. Later, opal became known as a powerful charm against insanity and also a potent tool for banishing evil and predicting misfortune.
Uses
Opal has a wide variety of uses in jewelry. It is often bezel-set, or cut in a variety of shapes and sizes. Cabochon-cut opal is also popular, and is often used to make pendants, earrings, and brooches. Opal can also be faceted and made into various shapes, such as ovals, marquise cuts, and hearts.
The opal is also used in beads, watch dials, and other decorative pieces. Opal is also used as an industrial abrasive and for decorative ornamentation.
Conclusion
Opal is one of the most fascinating and beautiful gemstones available today. Its colorful optical properties, range of hardness, and wide variety of uses make it an ideal choice for many different jewelry designs, as well as industrial and decorative applications.
