Gemstones are classified into two categories, precious and semi-precious stones. Traditionally the common precious stones are diamonds, rubies, sapphires and emeralds. This classification dates back to ancient times and is based on the rarity and beauty of the stones. Precious stones are usually more expensive than semi-precious stones.
Diamonds are often at the top of any jewelry shopping list and are reputedly ‘a girl’s best friend’ as endorsed in song by Marilyn Monroe. This still applies in the 21st Century as they are the stones given when an extra special jewelry gift is required. They may be a symbol of both love and surprisingly, infidelity, as it is often a gift used to appease a guilty conscience! Above all they are beautiful, expensive and make the wearer feel like a ‘million dollars.’
Diamonds are the hardest mineral in the world, registering at 10 on the Mohs scale of mineral hardness and are made up of carbon with their transparency giving a clear appearance. Choose a diamond by using a ‘4C’s’ guide – cut, clarity, carat and color. The carat determines the quality of the diamond. A diamond cut badly will make the appearance of it appear dull; the better cut will enable more light to be given off from the top of the diamond.
Unlike other precious stones, diamonds are a separate industry with diamond prices being set by world markets. 
Never buy any form of diamond without the ‘Diamond Certificate of Purchase’ document; this is mandatory and applies to every sale where diamonds are concerned.
Rubies have been recognized as a valuable stone for thousands of years and are beautiful red stones ranging in color from a rich dark claret red to a red with a pinkish or purplish tinge. They are a variety of the mineral corundum. Many rubies are heat treated to intensify their color and clarity. One description of a very valuable ruby is that of being ‘the size of a pigeon’s egg,’ and whoever had a ruby of this size would indeed be a very wealthy person. Rubies are said to reflect the vibrancy of life and the passion of love, although the giver may not be aware of this last attribute!
They register at 9 on the Mohs scale of mineral hardness. The cut and carat determine the price, and a truly valuable ruby may be more expensive than a diamond.
Burmese rubies are considered to be among some of the best in the world with other country sources being Vietnam, Thailand, Sri Lanka, Madagascar, Kenya and Afghanistan. 
Rubies may also be produced under laboratory conditions which result in a passable but cheaper version. It is advisable to purchase from a known dealer or jeweler, as they will be able to provide a history of any treatments that may have been carried out as well as providing a certificate of authenticity.
Sapphires, like rubies, are a variety of the mineral corundum and have been said to be the blue version of rubies. Blue is the classic color associated with sapphires although they can be yellow, pink or green. These are less popular. Sapphires, too, have a high scratch resistance and register at 9 on the Mohs scale. 
Look for a really beautiful medium shade of blue that is neither too dark nor too light to obtain maximum stone value, although a light blue stone reflects a different kind of light.
Dark blue sapphires with diamonds are classic pieces of jewelry and will always produce an elegant, yet subtly expensive aura.
Emeralds are a beautiful green-colored stone. They are a variety of the mineral ‘beryl’ and it is the chromium content that gives them their exquisite green. Emeralds are quite durable, registering 7.5 on the Mohs scale of mineral hardness; however, they may develop internal flaws if knocked. They are similar to diamonds by having a 4C’s guide of color, cut, clarity and crystal. The color may range from light to dark green; a good stone would be classed as having a medium to dark tone with great clarity.
Emeralds are well known for having flaws so it is advisable to purchase from a reputable dealer who will know the history of the stone. Colombian emeralds are amongst some of the best in the world, and high-quality emeralds may be more expensive than diamonds. They may also be found in Brazil, Zambia, South Africa, Zimbabwe, India, Afghanistan, Pakistan and Russia. 
Jewelry often speaks louder than words, and none speaks louder than precious stones. Choose them wisely and enjoy them.