In order to determine the karat weight of a specific item, simply look for the quality mark. Jewelry items will bear the stamp of their karatage based upon the United States or European system of marking. The United States system designates pieces by their karats—24K, 18K, 14K, 10K, etc. The European system designates pieces by their percentage of gold content. For instance, 10K gold is marked “417,” denoting 41.7% gold; 14K is marked “585,” denoting 58.5% gold; and 18K is marked “750,” denoting 75% gold; etc.

Opal
Known for its fiery combination of colors, opal is called the "Cupid stone" because it was said to reflect the complexion of the Greek god of love. The ancient Romans believed the gem was the symbol of hope, good luck and purity. Today, it remains a symbol of hope and inspiration. With a name stemming from the Latin word for "precious stone," opal is considered October's birthstone and is traditionally given as a 14th anniversary gift.

Opals are luminous and iridescent stones with inclusions of many colors called "fire." It is sometimes called the "queen of gems" because it can flash patterns of color representing every hue of the rainbow. In fact, most stones are usually cut into domed cabochons to enhance the color play. The brilliance and pattern of an opal's fire determines its value. Opals with strong flashes of red fire are generally the most prized, while stones with blue or green flashes are more common and subsequently less valuable. Stone size also helps determine price, since the gem is very rare in larger sizes.

In order to produce a stone that is less expensive than a solid opal, an opal doublet can be manufactured. It is composed of a thin layer of opal glued on top of another mineral (usually a black onyx or ironstone, which enhances the opal's color). An opal triplet can be made with a thin layer of opal sandwiched between a layer of clear quartz on top and a layer of obsidian or ironstone on the bottom. The clear quartz top layer makes the gem harder and less susceptible to scratches. Since top-quality natural opals are extremely rare and expensive, many are treated with colorless oil, wax or resin to enhance their appearance. Ranking a hardness of 5.5-6.5 on the Mohs Scale, these treatments also fill cracks in the stone to improve durability.

A species of quartz, opal is one of the few gemstones that are sedimentary in origin. Millions of years ago, after ancient seas receded, silica-laden sediment was deposited around shorelines. Erosion made much of this silica into a solution that filled cracks in rocks, clay and fossils. Layers upon layers of silica jell were added to each other over millions of years and became precious opals. The stones still contain 6 to 10 percent water, a remnant of ancient seas. Because they have high water content, opals should be protected from heat and strong light in order to prevent them from drying out and cracking.

Opal is found in a range of hues, including white opal (the most common), black opal (the most valuable), boulder opal (black opal with iron oxide), crystal or water opal (which is transparent), and fire opal (which features a bright solid color). The body color determines the variety of opal and has a large impact on the value.

White opals tend to have more diffused fire due to their light background color. Rare black opals have a black to dark gray body color that allows for the fire to be the most noticeable, making them the most valuable type of opal. Boulder opals are cut with the natural host rock left on the back. They are found with interesting hills and valleys on the surface and inclusions in the foreground, forming odd shapes that make them a designer's delight. Crystal opal is transparent with flashes of rainbow colors, while fire opal only occasionally has this play of color. Fire opal's backdrop color is the main attraction. With bold yellows, oranges or reds, it is usually faceted to add sparkle and enhance the fabulous color.

The vast majority of the world's opal supply comes from Australia, first discovered there by gold panners in 1863. In addition to a small quantity of opal produced in Kenya and Canada, white opal is mined in Brazil, black opal is found only at Lightning Ridge in Australia, crystal and fire opal can be found in the United States and Mexico, and a blue-green opal is found in the Andes Mountains of Peru.

Opals have been treasured for thousands of years throughout the world. The gem was loved and highly valued by the Romans, who called it "opalus." In fact, a beautiful opal called the "orphanus" was featured in the crown of the Holy Roman Emperor and was said to guard the regal honor. The Aztecs mined opal in South and Central America and archaeologist Louis Leakey found 6,000-year-old opal artifacts in a cave in Kenya. Napoleon gave Josephine a beautiful opal with brilliant red flashes called "The Burning of Troy," making her his Helen. To this day, opals are still set in the crown jewels of France. Queen Victoria loved opals and often gave them as wedding gifts. She was one of the first to appreciate opals from Australia and, along with her daughters, created a fashion for wearing the gemstone.

There are also several literary references to the fascinating stone throughout history. Shakespeare regarded opal as a symbol of shifting inconstancy, comparing its play of color to play of mind. In "Twelfth Night" he wrote, "Now the melancholy God protect thee, and the tailor make thy garments of changeable taffeta, for thy mind is opal." In the 19th century, Sir Walter Scott caused a reputation that opals were unlucky. The heroine of his popular novel had her life force caught in the opal she wore in her hair and died when its fire was extinguished.

For thousands of years, opals have been revered for their supposed mystical powers. Romans thought the stone kept the wearer safe from disease and wore it near the heart on necklaces to ward off evil and protect travelers. Ancient Arabs believed that opals fell from heaven in flashes of lightning, which explained their fiery colors. During the Middle Ages, opal was called "ophthalmios," meaning "eye stone," due to a widespread belief that it was beneficial to eyesight. Some thought its effect on sight could render the wearer invisible, and the stone was even recommended for thieves. In medieval Scandinavia, blonde women wore opals in their hair to prevent it from going grey.

Today, opals are still believed to hold magical powers. White opals, when used in rituals on a full moon night, are said to bring the moon goddess' powers into full effect within the practitioner. Specially shaped black opals are often worn on gold jewelry to further enhance their magical properties and powers. A fire opal surrounded with 10 or 12 diamonds and worn on a gold necklace is said to have excellent money-drawing power.

Opals have been said to bring good luck, grant vigor and ideally protect travelers. The stones have long been believed to develop and increase mental capacities and open the unused powers of the mind. The colorful fire in opals is said to develop a more creative imagination and help recall past lives. It is believed that the most magically powerful opals come from Lightning Ridge in Australia and that the gem loses its power once its owner dies.

Tanzanite
No other gemstone discovery has made a bigger impact on the jewelry market than the recent newcomer, tanzanite. Its luscious color, and the fact that the stone is found in only one location throughout the world, makes tanzanite an exceptionally rare, valuable and highly sought-after gem.

Tanzanite’s mesmerizing saturation of color is what has made the stone so popular. It is the blue variety of the mineral zoisite and occurs in a beautiful range of colors. Rarely pure blue, the gem almost always displays signature overtones of purple. In smaller sizes, it tends toward light tones such as lavender, while in larger sizes, the gem typically displays deeper, richer blues and purples. The finest quality tanzanite is usually deep blue or violet, which is extremely spectacular in sizes above ten carats.

Tanzanite is pleochroic, meaning it shows the appearance of several colors in the same stone, depending on perspective. From different angles, the gem can appear blue, purple, yellow, grey or brown. Most rough crystals show a large proportion of brown shades, since tanzanite in its natural form is typically brown with red, orange, yellow or bronze hues.

Gem cutters may change this coloring by heating the stone to 500°C. This heat treatment releases the intense violet-blue colors for which the stone is famous. According to legend, the effect of heat on tanzanite was first discovered when brown zoisite crystals were caught on fire by a lightning strike. Local cattle herders noticed the beautiful blue crystals sparkling in the sun and picked them up, becoming the first tanzanite collectors.

The gem was first discovered near the base of Mount Kilimanjaro in the Merelani Hills of east-African Tanzania in 1967. This breathtaking location is the only known mining site on Earth for tanzanite. Right after its discovery, New York jeweler Louis Comfort Tiffany was presented with the first stones. Knowing it was going to be a sensation, he recommended finding a new name for the gem, since the gemological denomination “blue zoisite” reminded him of the word “suicide.” Tiffany suggested the name tanzanite, derived from its place of occurrence, and the new name quickly became established on the market. Tiffany & Co introduced the stone to the public in a spectacular promotional campaign two years after it had been discovered. It was enthusiastically celebrated as the “Gemstone of the 20th Century.”

A noted 122.70ct faceted tanzanite dubbed the “Midnight Blue” is on display at the Smithsonian Institution in Washington, D.C. In 1996, a 255.00ct tanzanite crystal was discovered near Arusha, but because of its many inclusions, it proved to be of little market value. Tanzanite ranks a hardness of 6.5-7.0 on the Mohs Scale and has become the traditional gift for couples celebrating their 24th anniversaries.

High-quality and larger-size tanzanites can be sold at extremely premium prices. Although demand for this beautiful gem continues to grow, supply shortages in recent years have hampered production and caused price fluctuations. In 1998, the weather phenomenon known as “El Nino” soaked Tanzania with heavy rains during what should have been the drought period. When the monsoons hit, the groundwater swells were high and caused devastating floods. Mines caved in and all hopes of finding additional tanzanite rough were swept away.

Because it is such a new gemstone, there is little folklore, superstitions or healing properties surrounding tanzanite. Some believe the stone helps people to be more practical, realistic and honest. It is thought to uplift and open the heart while helping one cope with change.