Types of Opals - Characteristics, Healing Properties and Other Facts
Chemical Composition & Hardness
Chemically, opal is silicon dioxide plus water. It has a chemical composition of SiO2.nH2O. The water content is usually ranges from 3% to 10%. Therefore it is noncrystalline, unlike most other gemstones. As opal contains a high percentage of water, it may deteriorate in cold and heat. Opal hardness varies, but generally ranges from 5.5 – 6.5 according to Mohs scale of harness. There are many types of opal such as crystal opal, black opal, white pal, boulder opal, yowah nut opal and matrix opal.
Opal is the most colorful of all gems. The stone is usually green, white or colorless, but it may be brown, gray, red and yellow. Opal has a rich iridescence and extraordinary or remarkable play of changing colors, usually in green, blue and red. This phenomenon is often called opalescence. The arrangement of silica spheres within the opal create these colors. The play of color may consist of tiny, dense flashes of color, or large individual flashes (known as schilers). The value of an opal is determined by the distribution and intensity of the color flashes. Opals with milky-white base with varying flashes of color are the opals we see most often in jewelry.
Opals which lacking play of color are known as common opals, and opals displaying play of color are known as precius opals. Gems are cut from both the common and precious forms, but precious opal is the primary gem of this stone. The most valuable and desired opal is black opal (a dark green, dark blue, or black background with a strong play of color). Some precious opals are even more valuable per carat than diamonds. Most opals including black opals come from Australia. Opals are also found in western United States, Mexico, Africa, Brazil, Nicaragua and areas of the former Soviet Union. Six-thousand years old opal adornments was found by an archaeologist, Louis Leakey in a cave in Kenya. French Emperor Napoleon gave opal called ‘The Burning of Troy’ to his wife Josephine because of its strong play of colors.
Opal is also believed to have mystical, healing and magical properties. It is a stone of inspiration which enhances the creativity, memory and imagination. Opal is associated with the heart, and told to regulate the metabolism and stimulate the glands. The ancient Greeks believed this stone could give to the wearer the power of foresight. Opal was revered by the Romans as the symbol of purity and hope and they believed the gem could protect them from diseases. Opal was thought to be beneficial for eyesight in the Middle Ages, some people even believed the gem could render the wearer invisible.
Opal is the birthstone for those born in the month of October and goes by the title “The Queen of Gems”. These stones was once considered unlucky, but this is probably due to the fragility of the stones and tend to scratch and chip easily. The stone should be protected from strong light and heat, which can dry the water out, causing cracks. Acids, ultrasonic cleaners, or any strong solvents should also be avoided.