100% Natural - Not treated in any way. Ideal for Designer Jewelry. Gem with High Luster and Good Clarity. Large Sizes are Extremely Rare! Refractive Index: 1.544 - 1.553 Hardness: 7 Chemical Comp: SiO2 Density: 2.66 Crystal Group: Hexagonal Ametrine belongs to the larger Quartz family and is a very popular gem for jewellery manufacturers due to the availability in large sizes at affordable price.Bi-Color Yellow and Purple Quartz gemstones are called Ametrine.Ametrine can also be cut to blend both colors so that the result is a mixture of yellow, purple, and peach tones throughout the stone.