Gahnite, also known as zinc spinel, is a rare type of mineral that typically occurs in metamorphic and igneous rocks. There are not many synonyms for gahnite, but it is sometimes referred to as octahedrite, due to its crystal structure, or as zinc aluminate spinel, to indicate its chemical composition. Gahnite is prized by mineral collectors for its blue-green to black color and its durability, which makes it ideal for use in high-temperature applications. This mineral can also be found in some gemstones, such as the blue-green gahnite found in Australian sapphires. Despite its unique properties, gahnite remains relatively unknown to the general public.