Along with sapphires, rubies are the second hardest substance on the Mohs scale. This is because both gemstones are corundum. Ruby is red corundum, while sapphires make up all other color variations of corundum.

The ruby is a very rare and precious gemstone. A ruby's rich color, hardness, and silky shine secure this position. Indeed, color is the most important deciding factor in a ruby's value. The clarity is not as important in this process. The most desirable color in a ruby is that of pure red with just a hint of blue. This is extremely rare, and one of the most expensive of all gemstones. Here, color saturation is the determining factor in value and cost. The most desirable light to view rubies in is daylight. Inclusions in rubies are common and do not necessary indicate a lower quality stone. Again, color is the deciding factor in quality and value.

Emerald is part of the beryl group of gems, and is among the four traditional precious stones, the others being sapphire, ruby, and diamond. It is the most precious stone in the beryl group.

The emerald is a fragile stone because of its many natural inclusions. The color of the emerald is the most important factor when determining value. The most popular and valuable color is a slightly bluish green in a medium dark tone with strong to vivid saturation. An emerald definitely looks best in daylight, but artificial light will indeed expose all inclusions that absolutely prove the stone to be natural. So, it is best to test it out in both types of light. This being said, inclusions in emeralds, unlike in most any other gemstone on earth, are preferred and add more value to the stone.

Tanzanite is a relatively newly discovered gemstone. In 1967 it was discovered in the only deposit still on earth ...Tanzania. Tiffany & Co. was the first jeweler to market this stone as a fine gemstone in the industry. It is not a very hard stone, which throws caution to the wind when wearing it. It should be handled with care.

The most valuable and sought-after color for tanzanite is that of ultramarine to sapphire blue with a shimmering violet hue around it. To achieve this color, nearly all tanzanite is heat-treated. Daylight is the best way to view a tanzanite stone.

This is the most famous and expensive of all garnets. The African Tsavorite garnet was recently discovered in 1967 in East Africa. It has an emerald-like green color but is much more vivid and brilliant due to a higher refractive index. Tsavorite's are also much more durable than emeralds.

Tsavorite is extremely rare, and are found only in Tanzania, Kenya, and Madagascar. They are 200 times rarer than emeralds! Tsavorites are always left untreated.

Tourmalines occurs in more colors and combination of colors than any other gemstone variety on earth. Tourmaline started its popularity when the Dutch started importing it in the early 17th century from Sri Lanka.

When viewing tourmaline, reds, oranges and yellows will look best under incandescent light, while greens, blues and violets look their best under daylight. Large crystal sizes enhance the depth and richness of color. Most tourmalines are left untreated.

Aquamarine is part of the beryl group and is appreciated for its soft blue or blue-green color. It has good hardness and luster. It is a beautiful stone where the more saturated the color, the higher the value.

The most desirable and valuable aquamarines are those that have no inclusions, are clear and transparent. Most aquamarines are heat-treated so as to achieve the desirable blue-green colors. Brazil serves as the host to most aquamarine mines in the world. The United States also has several mining locations.

Amethyst is by far the most precious gem in the quartz group. It is transparent purple quartz with much historical royal importance. Purple is the color of royalty, and amethyst served as an important gemstone in this realm. Amethysts were featured in British crowns, Egyptian royalty, and the bishops within the Christian church.

A deep purple amethyst is the most valuable of amethysts with the Siberian Amethyst displaying a deep purple with red and blue flashes as the highest priced amethyst. Soft and warm tones of daylight are the best to view amethyst in. The most valuable amethyst is free of inclusions and is transparent in show. Brazil has the largest deposits of amethyst in the world.

Pure topaz is transparent and colorless. The wide range of topaz colors available in the market is a result either of natural trace impurities or defects in the crystal structure, or enhancements by the gemstone industry. Topaz come in many different colors including yellow, orange, brown, red, blue, pink, red, violet and green.

The most popular color, blue, is a very rare find in nature. Even then, it is pale in color. Thus, most all blue topaz is heat-treated so as to produce the illuminating, striking shades of blue that is seen on the market. There are three shades of blue that are produced: the deep blue, the saturated medium blue, and the bright light blue.

Although blue topaz is the most popular topaz on the market, the most valuable and expensive topaz is the Imperial Topaz, which is an orange to pink color. Topaz is a good stone, with a good hardness to it as well as high refractive index. It is also not sensitive to chemicals.

This stone is one of the most affordable AND most popular stones! Typically, gold in color, it also comes in orange brown and red shades of transparent quartz. Natural citrine is mostly pale yellow to golden in color.

Most citrine found in the market is heat-treated amethyst, and thus has a reddish tint. Though most citrine is heat-treated, the most sought after and valuable are indeed the natural citrine stones. This at least makes it easy to determine what citrine stones are natural and which are heat-treated. The chief determinants in value are color, clarity, and luster. Since citrines are transparent, it should be fairly easy to determine the clarity.

The largest natural deposit of citrine is in Brazil, while other sources are found in Argentina, Madagascar, Myanmar (Burma), Namibia Russia, Scotland and Spain.

Alexandrite is part of the Chrysoberyl family of gemstones. Alexandrite, the rare color-change variety, is green in daylight and reddish in artificial incandescent light.

Known for its brilliance and luster, clean stones are the most valuable of this gemstone family. Alexandrite deposits are in Brazil (Minas Gerais), Madagascar, Myanmar (Burma), Sri Lanka and Tanzania. The largest cut alexandrite, 66ct, belongs to the Smithsonian Institution in Washington D.C.!

The hardest gemstones on earth, diamonds have been treasured as gemstones since their use as religious icons in ancient India. The popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds.

Diamonds also come in a variety of natural colors; fancy yellow, chocolate brown, colorless white, blue, green, black, bubble gum pink, orange, purple, and red. "Black", or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless.

Historically, diamonds were found only in deposits in Guntur and Krishna district of the Krishna River delta in Southern India. Today, diamonds can be found in Arkansas, Colorado, Wyoming, and Montana. They are also mined in Russia, Australia, Canada, Zimbabwe, Angola, and the Congo.

Chalcedony is a form of quartz. It refers to any translucent, cryptocrystalline quartz with a single color. The colors of chalcedony are bluish, white, or gray. Chalcedony has different species. The most popular are the bloodstone, the blue chalcedony, and the carnelian.

The bloodstone is dark green in color with red spots. It is opaque. The blue chalcedony is mainly from the western United States. These stones are gray blue with a light-to-medium color range. They can also have moderate amounts of pink. The blue chalcedony that is found in Africa is gray to nearly clear blue in color.

Carnelian ranges in color from yellow orange to rich, near reddish orange, to orangey brown, and varies from semi-opaque to highly translucent. Cornelian onyx is a layered stone with a red base and a white upper layer. In all chalcedony, the saturation of color determines the quality and value. The clarity is anywhere between translucent to opaque and is dull in luster.

Spinel is the newest birthstone for August. It is singly refractive like a diamond and has a lot sparkle when faceted. Spinel is a durable natural gemstone which is usually untreated and available in a wide variety of vibrant colors. The most popular color of spinel being red and blue. The red spinel throughout the ages has often been confused with ruby. Red spinel, however, is less expensive than ruby.

In history, the faceted gemstones long believed to be rubies in the British Imperial State crown and the European Crown of Jewels are actually red spinel. Spinel are available in yellow, pink, red, blue, black, purple, and white. The more vivid, vibrant blue are the rarest of the color and tend to be the most expensive.

These stones can be found in Sri Lanka, Myanmar, Thailand, Viet Nam, Russia, Kenya, Cambodia, Madagascar, Pakistan and the U.S.A. It is believed that when worn, the stone enhances creativity, cognitive abilities, and increases protection.