Sterling Silver Tanzanite Pendant (1/2 CT) With 18 Inch Chain 30 Day Easy Returns. Jewelry Gift Box Included .925 Sterling Silver Natural Tanzanites are heat treated to produce a range of hues between bluish-violet to violetish-blue. This is done through mild heating in the production process. Due to the permanent nature of this treatment the gemstones do not alter in quality, only in appearance. 18 Inch .925 Sterling Silver Chain Included