Rare Natural Thai Black Star Sapphire. No treatment. 3.78 Carat Dimensions.10.2x8.5x3.6 mm. This item has inclusion. A star sapphire exhibits a star-like phenomenon known as asterism; red stones are known as "star rubies". Star sapphires contain intersecting needle-like inclusions of rutile this cause the appearance of the "star"-shaped pattern when viewed with a single overhead light source. The inclusion is often the mineral rutile, a mineral composed primarily of titanium dioxide.[8] The stones are cut cabochon, typically with the center of the star near the top of the dome. Twelve-rayed stars are occasionally found, or parallel whisker inclusions can produce a "cat's eye" effect. The Black Star of Queensland is believed to be the largest star sapphire that has ever been mined, and it weighs 733 carats. (We use DHL registered Singapore post and Australia post all items are posted in Australia.) Disclaimer. We use natural sunlight when we can. We also use lights that produce as close to possible natural daylight. We use photo shop to cut and edit but not to enhance. We also know many computer screens buyers use, vary greatly along with their eye sight. You get the products we sell at a very good price because we buy in bulk. Gems and opals especially need light sometime strong to see their wide ranges of colors and color play So make sure you have a good source of light when examining them. Cheers and thanks for your support.