The precious stone known for its deep blue color is sapphire. Sapphires are a variety of the mineral corundum and come in various colors, but the blue hue, developed by trace elements like iron and titanium, is the most celebrated. This gemstone has been prized since ancient times, symbolizing wisdom, loyalty, and nobility. Sapphires are often used in fine jewelry, including engagement rings, and have significant cultural and historical importance in various cultures. The rich color and durability of sapphires make them a favorite among gemstone enthusiasts and collectors.