a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Because of its amorphous character it is classed as a mineraloid, unlike the other crystalline forms of silica which are classed as minerals. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent. Opal’s hardness is 5.5 – 6 on Mohs scale.
The name opal was probably derived from Sanskrit “upala”, meaning “valuable stone” or from the Greek word “opallus” which means to see a change in color. Later, the Latin word “opalus” evolved, meaning precious stone. In the days of Roman antiquity there existed a so-called “opalus”, or a “stone from several elements”. Pliny the Elder, the famous Roman author, called opal a gemstone which combines the best possible characteristics of the most beautiful of gemstones; the fine sparkle of almandine, the shining purple of amethyst, the golden yellow of topaz, and the deep blue of sapphire, “so that all colors shine and sparkle together in a beautiful combination”.
For ages people have believed in the healing power of opal. It is reported to be able to solve depression and to help its wearer find true and real love. Opal is also said to stimulate originality and creativity. Opal is porous and because of this, it is quite absorbent. Due to its ability to absorb, it is thought that it can pick up the thoughts and feelings of people and amplify emotions. Opal is a birthstone for those who are born in October.
Opals are delicate gemstones. Their most significant weakness has to do with their water content. If an opal is allowed to dry, it will crack and fade. If you live in a very dry climate, or keep them in a dehumidified room, some precautions are necessary. Keeping them in a tight plastic bag, with a damp piece of cotton or fabric will prevent dehydration. Because of their water content, opals are also highly sensitive to sudden changes in temperature.
Being somewhat soft, opals scratch easily. It is important to realize that a large component of ordinary dust is quartz at 7 (Mohs scale) in hardness. At 5.5 to 6 in hardness, simply wiping the dust off an opal will gradually reduce its polish. The solution is to clean your opals using a soft cloth and only mild soap or detergent if needed. Do not use harsh chemical or cleaners and avoid ultrasonic cleaners and steamers. Always remove opal jewelry before engaging in vigorous physical activity.