Sapphire, derived from the Latin word "Sapphirus" meaning blue, belongs to the corundum group of minerals in the trigonal crystal system. In the gemstone industry, all colors of gem-grade corundum other than rubies are classified as sapphires.

The primary component of sapphire is alumina (Al₂O₃). When corundum contains trace elements such as iron (Fe) and titanium (Ti), it exhibits various colors including blue, sky blue, and light blue, with bright sky blue being considered the most desirable.

Lab-created sapphires are virtually identical in appearance and properties to natural sapphires, making them difficult to distinguish without specialized equipment. Identification typically relies on examining internal characteristics, where synthetic sapphires may contain bubbles or fine curved growth lines.