A star sapphire is a type of gemstone that exhibits a unique star-like pattern on its surface, known as asterism. This effect is caused by the presence of needle-like inclusions of the mineral rutile within the sapphire. When light hits the stone, it reflects off these inclusions, creating a star shape that can appear to move as the stone is rotated. Star sapphires are typically found in various colors, with blue being the most popular. They are a variety of corundum, the same mineral that forms regular sapphires. These gemstones are often cut into cabochon shapes to enhance their star effect, making them highly sought after in jewelry.