Cat Head Birthstone Rings. Looking to spice up your daily accessories while keeping your favourite gemstones close? These gemstone stretch rings, each with a natural shell cat head, look great and provide all of the positive effects natural gemstones have to offer! Because of the elastic design, these rings fit almost any finger! Available in 12 Birthstone Gems: January: Garnet February: Amethyst March: Aquamarine April: Clear Quartz May: Green Aventurine June: Moonstone July: Carnelian August: Prehnite September: Lapis Lazuli October: Rose Quartz November: Citrine December: Turquoise