A ruby is a variety of the mineral **corundum**. While pure corundum is colorless (known as white sapphire), the presence of specific trace elements during its formation creates vibrant colors. To be classified as a ruby, the stone must be red. All other colors of gem-quality corundum (blue, pink, yellow, etc.) are classified as sapphires. Color is the single most important factor in determining a ruby's value. Gemologists evaluate color based on three components: The primary red color, plus any secondary modifer (e.g., purplish red, orangey red). The most prized hue is a pure, vibrant red. How light or dark the color is (ranging from very light to very dark). Most valuable rubies are medium to medium-dark tone. The intensity or brightness of the color. The more vivid the red, the higher the value. This trade term is used to describe the absolute finest ruby color: a highly saturated, vibrant, pure red with a soft, glowing fluorescence. Historically associated with rubies from Mogok, Myanmar. Inclusions are internal characteristics (minerals, cracks, or liquids) trapped inside the gem. Unlike diamonds, where eye-clean clarity is crucial, inclusions are expected in rubies and often confirm their natural origin.