Star sapphire is a captivating gemstone known for its unique asterism, which is a star-like phenomenon that appears on its surface when light reflects off of it. This effect is caused by the presence of needle-like inclusions of the mineral rutile within the sapphire. When cut in a cabochon shape, the star effect becomes prominent, typically displaying a six-rayed star that moves as the stone is rotated.

The color of star sapphires can vary, with blue being the most common and highly sought after. However, they can also be found in shades of black, gray, yellow, and even pink. The best star sapphires exhibit a deep, rich color combined with a sharp, well-defined star.

In terms of hardness, star sapphires score 9 on the Mohs scale, making them extremely durable and suitable for everyday wear. They are often set in rings, pendants, and earrings, where their unique star effect can be showcased.

Star sapphires are also associated with various metaphysical properties, such as promoting wisdom, protection, and serenity. If you have any more questions about star sapphires or other gemstones, feel free to ask!