Garnet is typically thought of as a reddish gemstone, although it actually ranges from colorless to black. A fairly hard mineral, Garnet scores at about 7-7.5 on the Mohs scale of hardness. Garnet is the state gemstone of Connecticut and New York.
Amethyst is a fairly common purple to lilac gemstone, ranging in translucence from fairly opaque to the more highly valued and higher quality transparent stones. It is a purple variety of the quartz family, and it is the most valuable in its group. If left in the sun, amethyst will tend to lose its color, which can only be restored by a fairly expensive radiation process. Heat-treated amethyst may change to other colors, such as yellow (citrine), red, brown, green, or clear, at which point it is no longer properly called amethyst. Amethyst is the state gemstone of South Carolina.
Aquamarine is a light-to-dark-blue gemstone that ranges in opacity from translucent to transparent, the clearer gems considered higher quality and more valuable. A variety of beryl, aquamarine’s color comes from the iron inside. It pales if left out in the sun, although it is routinely heat-treated to drive out any green in its coloration to form a more pure blue. Aquamarine means “sea water” in Latin, and the stone is the state gem of Colorado.
Diamonds are viewed as special stones and are usually clear. However, due to the presence of impurities or other minerals inside, they may also be brown, yellow, green, blue, pink, red, gray, black, or purple. The diamond is the hardest mineral found in nature, having a hardness of 10 on the Mohs scale, and it is also one of the purest forms of carbon. The diamond is the state gem of Arkansas and the seasonal gem of Winter. Pure diamond is colorless, although the inclusion of other elements (like nitrogen) may alter the color of a diamond. Synthetic body color may be added to a diamond by means of heat and irradiation processes, which are permanent, and therefore considered legitimate. Such alterations, however, decrease the value of a naturally colored diamond. The diamond conducts heat better than any other mineral.
Emerald is a light-to-dark-green gemstone, a form of the mineral beryl that derives its color from the elements chromium and vanadium. It is often irradiated for clarity. Because emeralds grow in the limiting envirnonment of surrounding metamorphic rocks, large emeralds are particularly rare. Emeralds of a deeper green are more valued, and small inclusions are not as detrimental to the value of an emerald as they are to other gems. Emeralds are often oiled to improve their apparent clarity and to soften the appearance of inclusions. This process is routine and is generally not disclosed. Emerald is the state gemstone of North Carolina and is said to be the seasonal gem of Spring.
Not truly a gemstone, pearls are actually formed in
shellfish as a reaction to irritants like sand. Cultured pearls may be formed by
artificially placing irritants inside mussels. Pearls are generally white,
brown, silver, cream, black, or pink, depending on the type of shellfish that
created them and on the type of water in which the source shellfish lived. Their
prices vary widely as a result of lustier, size, nurturing method, color, and
type. Natural pearls are the most expensive, followed by cultured pearls, and
finally freshwater pearls. Pearls are relatively soft, having a hardness factor
of 3, and they are the state gemstone of Tennessee.
Ruby is a form of corundum, colored red by deposits of chromium and iron. Rubies are often heat-treated in order to permanently improve their color and clarity, and they have consistently been the most valued gem in history. The most expensive ruby, in fact, was a 16-carat piece sold for over $200,000 per carat in a US auction. Color is the most important characteristic of the ruby, a brilliant, deep red being the most valued color. Other criteria include clarity, with a transparent ruby being most valuable, cut, and, of course, size. The ruby is the Wisconsin state gemstone and is also said to be the seasonal gemstones of Summer.
Peridot is a lime-green-to-olive-green gemstone often worn on necklaces and earrings. It is created from volcanic eruptions and is sometimes even found on meteors that have fallen to earth. Its color is dependent on its body size, so the smaller stones cannot produce the intense greens prized in the larger ones. It is the state gemstone of Nevada and has a hardness-rating of 6.5 on the Mohs scale. Peridot is a fairly soft gem and is susceptible to attack by acids, which can quickly remove the polish from its surface.
Although usually thought of as being a blue gemstone, sapphires in fact come in every color except for red, when they are dubbed rubies. Actually corundum, sapphires may be blue, white, purple, yellow, green, pink, and orange, and they have a hardness factor of 9 on the Mohs scale. Some sapphires change color from blue to purple, depending on the light. The highest quality sapphires have an intense, vivid, blue shade, holding their color in all angles of light. Sapphires have become more readily available, as the colors of poor quality sapphires, such those of light, cloudy, or dark colors, may easily be transformed into a more desirable one by means of a process involving intense heat. This process is completely stable and is now almost regarded as routine. Because of its hardness, the sapphire is one of the most durable gems. Sapphire is the state gemstone of Montana and is also considered the seasonal gemstone of Autumn.
Opal is a shiny, variegated stone that reflects light in many different colors. Generally white, orange, or black, all opals have flecks of purple, red, green, and yellow dancing inside. Black opals with extremely dark body color have the most brilliant flashes of color and are the most valuable form of opal. Transparent opals are the next most valuable, as many layers of color may be seen inside their depths. Milky or white opals are the most affordable, but they tend to have diffused colors as a result of their light background. Water may compose up to 30% of an opal’s content, and drying out an opal may cause cracking. The Virgin Valley Black Fire Opal is the state gemstone of Nevada.
Topaz is a typically light-blue gemstone, but it may also
be found in blue, yellow, pink, brown, green, and clear. “Imperial” topaz, which
is orange-red, is the rarest variety, and therefore the most valuable. The color
of a clear topaz gem may be transformed into other colors by means of an
irradiation and heat-treating process; for instance, blue, yellow, and brown
topaz may be heat-treated to become pink, as natural pink topaz is relatively
rare. Topaz has a hardness of 8 and is the state gemstone of both Utah and
Turquoise is a vibrant light-blue-to-green gemstone with a hardness of 7 on the Mohs scale. It is often fracture sealed, which means it is shielded by a layer of acrylic resin to enhance its color, texture, and hardness, not that it has fractures. Turquoise made in a laboratory has a very uniform color, and chalky varieties of turquoise are often coated with wax or oil to enhance their color. When thus treated, the color change is not permanent. Under heat (roughly about 500 degrees Celsius), blue turquoise will adopt a greenish hue. Turquoise is porous and will absorb oils over time, gradually changing to a yellowish color.