Rich blue violet color on this super Tanzanite pair. Rich blue in one light, lilac blue in another. Tanzanite is trichroic which means when viewed in various orientations, different colors result.Tanzanite looks different in different lighting situations. Sunlight usually makes it look more purple. Light bulbs and candlelight also bring out the purple and can make the grayish ones look brown. Fluorescent lights tend to bring out the blue more, as do overcast skies on this.6.2x4.2mm and 6x5mm pair.
This gemstone (or gemstone that is part of this piece of gemstone jewelry) has been enhanced by traditional heat treatment. Traditional heat treatment is used to improve a stones color, remove color zoning/banding, and improve clarity. This treatment is considered permanent. The only way to tell if a colored stone has been treated is for the stone to be analyzed by a lab. Generally only gemstone laboratories have the equipment necessary to make a qualified judgement with any certainty.
Untreated gemstones are rare and should be verified by a lab independent of the seller. A good rule of thumb is to always assume a gemstone has been enhanced, unless valid certification from a reputable laboratory is available. No one that sells jewelry or gems should be doing appraisals, certifications, or analysis. It should always be an independent third party with no vested interest in the sale.