Star garnets are so rare that to date they have only been found in two places in the world; in the state of Idaho in the USA and in India. The garnet varieties that occasionally exhibit asterism are almandine and a mixture of almandine and pyrope garnet.
Star garnet gemstones are usually opaque and deep brownish-red or reddish-black. Like all star gems, the star effect is caused by inclusions of rutile. In order to display the star effect, the rutile needles must have the correct alignment to reflect light in a pattern forming a mult-rayed star.
Most star garnets display a 4-rayed star, but 6-rayed stars are sometimes seen. Some gemstone dealers claim that only the Idaho star garnets ever display a 6-rayed star, but this claim is difficult to verify since specimens with 6-rayed stars are very rare.
The people of Idaho are so proud of their star garnet deposits that star garnet has been declared the state gemstone. Star garnets are mined in Northern Idaho in a region that is northeast of Moscow and southeast of Coeur d'Alene.
The star effect in most star garnet gemstones is subtle and requires the correct lighting to be seen clearly. The best lighting is direct sunlight. However, a light source such as a narrow beam halogen spotlight or small flashlight will also work. The star is best seen by standing directly above the stone and looking straight down.