The Birthstone for December is Tanzanite. This necklace has 3 Tanzanite colored Swarovski Austrian Crystals representing the birth month. It is also made with black Magnetic Hematite beads. There are 5 sizes to choose from, ranging from 15 1/8 inch to 18 1/8 inches. Sizes are approximate and may vary by an 1/8 of an inch due to being hand made.