The diamond has always been the king of jewels and enjoyed tremendous popularity over the ages. However , there are a few other gemstones as well, that, like the diamond, can be classified as precious stones. These are the ruby, the sapphire, and the emerald. The pearl is also often included in this category, although strictly speaking, it is not a precious stone.

Ruby

The ruby is composed of the mineral corundum (aluminium oxide), with its characteristic red color due to the presence of chromium. Its name originates from ruber, Latin for red. Price i determined by color, with the brightest and most valuable "red", called pigeon blood-red, commanding the highest numbers. After color, clarity dictates price with the clearer stones being more expensive . The Mogok Valley in Upper Myanmar (Burma) has for centuries been the source for the best rubies, but reserves have depleted. One of the worlds largest and finest rubies, at 23.1 carats, was donated by businessman and philanthropist Peter Buck to the Smithsonian.

Sapphire

The sapphire (from Greek sappheiros, meaning blue), like the ruby, is also a variant of the mineral corondum. Although blue is the most well known hue, sapphire is any color of corundum except red. Purple sapphires contain trace amounts of vanadium while those with titanium are colorless. Iron impurities contribute to a green color. If both titanium and iron are present , the sapphire is colored a brilliant blue. Many of the famous sapphires are of Sri Lankan origin, while Madagascar is also a common source. The 423-carat Logan Sapphire at the Smithsonian is one of the most famous such stones in the world.

Emerald

The emerald (from Semitic izmargad, meaning green) is a variety of the mineral beryl, with trace impurities like chromium and vanadium contributing to its green color. In ancient times, emeralds were mined in Egypt and Austria. Now they mostly come from three main emerald mining areas in Colombia. In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. It is also commonly used to commemorate the 20th and 35th wedding anniversaries. The Gachala Emerald, a 858-carat stone donated to the Smithsonian by New York jeweler Harry Winston, is one of the largest emeralds in the world.

Pearl

The pearl is a gem created within the soft tissue of a living shelled mollusk. It is made of calcium carbonate in minute crystalline form, deposited in conentric layers. Natural pearls are created accidentally when a small enters a shelled mollusk and settles inside. The mollusk, irritated by the intruder, forms a pearl sac of external mantle tissue cells and secretes the calcium carbonate to cover the irritant. This secretion process is repeated many times, thus producing a pearl. Perfect natural pearls are extremely rare and strings can sell for hundreds of thousands of dollars.