Sterling Silver 5 Stone Light Tanzanite Earrings 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. The Tanzanite stones are very light in color.