Ruby is the red variety of transparent corundum and is one of the most prized precious gemstones. All colors of corundum are known as sapphires except red, which can cause doubt about where ruby ends and sapphire begins, particularly in pink shades. Lighter shades of reddish hues, however, should be included in the ruby category. The birthstone for July, the finest rubies are more costly than diamonds of the same size and are exceeded in value only by the emerald. Today, rubies are still more rare and valuable than even top quality colorless diamonds. Thailand is the world's most important ruby trading center, with up to 80% of the world's supply going through the country during the trading cycle.