Yes, tanzanite changes color, and it does so in two distinct ways. The stone shifts between blue, violet, and burgundy depending on the angle you view it from, and it also appears different under various lighting conditions. This isn’t a flaw or a sign of a fake stone. It’s one of tanzanite’s defining characteristics and a big part of what makes it unusual among gemstones.
How Tanzanite Shifts With Viewing Angle
Tanzanite belongs to a small group of gemstones that are “trichroic,” meaning they display three different colors depending on which direction light passes through the crystal. Along one crystal axis, the stone appears purple or bluish purple. Along a second axis, it looks green-blue to green-yellow. Along the third, it shows yellow to yellowish orange. These three colors exist simultaneously within the same stone, and which one you see depends entirely on the angle of observation.
This property, called pleochroism, happens because the crystal structure absorbs light differently along each of its three internal axes. When a gem cutter shapes a tanzanite, they choose an orientation that emphasizes the most desirable color. That’s why most finished tanzanites look predominantly blue or violet rather than green or yellow. But tilt the stone in your hand, and you’ll catch flashes of its other pleochroic colors. Exceptional tanzanites display an intense violet-blue with red flashes visible as the stone moves.
How Lighting Changes Tanzanite’s Appearance
Beyond the angle effect, tanzanite also responds to the type of light hitting it. Under natural daylight or daylight-equivalent bulbs, the blue tones come forward. Switch to incandescent (warm, yellowish) lighting, and the stone shifts toward violet or purple. Some individual stones are more “moody” than others, showing dramatic shifts between environments, while others stay relatively stable. This light sensitivity is separate from the angle-based color shifting and adds another layer of visual complexity.
This behavior is sometimes compared to the famous “alexandrite effect,” where a gemstone looks one color in daylight and another under incandescent light. Tanzanite’s light-source shift is generally subtler than alexandrite’s, staying within the blue-to-violet range rather than jumping between entirely different color families. Still, it’s noticeable enough that the same ring can look distinctly different at a candlelit dinner versus outdoors on a sunny day.
What Causes the Color
Tanzanite is a variety of the mineral zoisite, and its color comes from trace amounts of vanadium within the crystal structure. These trace elements absorb certain wavelengths of light (particularly around 460 nanometers, in the blue portion of the spectrum) at different intensities along each crystal axis. That uneven absorption is what produces the three distinct pleochroic colors rather than a single uniform hue.
Most tanzanite on the market has been heat treated to enhance its color. In its natural, unheated state, tanzanite often shows more prominent green, yellow, and brownish tones alongside the blue and purple. Heating the stone to around 500 to 550°C for roughly 30 minutes reduces or eliminates those brownish and yellowish components, pushing the color firmly into the blue-violet range that buyers prefer. The pleochroic nature of the stone remains after heating, so you’ll still see color shifts with angle and lighting. The treatment simply narrows the palette toward the more desirable end of the spectrum.
How Color Affects Value
A deep, saturated blue is the most sought-after tanzanite color, though some buyers prefer an intense bluish purple. Because the blue color tends to align with the shortest axis of the raw crystal, cutting a large stone that faces up blue means sacrificing more material. Blue tanzanites are therefore rarer and command a higher price than purple ones of the same size.
Paler stones are more affordable, and color saturation is the single biggest factor in tanzanite pricing. There is no universal grading scale for tanzanite quality. Some retailers use labels like AAA, AA, or A, but these are company-specific designations, not industry standards. The GIA does not maintain a standardized quality grading system for tanzanite the way it does for diamonds. When shopping, trust your eyes under multiple lighting conditions rather than relying on a letter grade.
What to Expect When Wearing Tanzanite
If you own or are buying tanzanite, the color shifts are something you’ll notice regularly. The stone will look bluer near a window, more violet under a warm lamp, and may flash burgundy or purple as it catches light from different angles on your hand. None of these shifts indicate a problem with the stone. They don’t affect its durability or value. Many tanzanite owners consider the shifting colors the stone’s most appealing feature, since it essentially gives you multiple looks from a single gem.
The color you see in a store may not match what you see at home, precisely because the lighting differs. If you’re purchasing tanzanite, viewing it under both cool (daylight-type) and warm (incandescent) light before buying gives you the most accurate sense of how the stone will behave in your everyday life.