Tanzanite color chart: shades, names and which color is finest
By HeyGema™ · Updated
In short
Tanzanite is the violet-blue to blue-violet variety of the mineral zoisite. A deep, saturated violet-blue or blue-violet is the most valuable, and paler hues are more common. A round 1 carat tanzanite measures about 6.6 mm.
- 4shades on the chart
- 6.6 mm1 carat, round
- 6.5 to 7hardness (Mohs)
Tanzanite colors
Tanzanite is the violet-blue to blue-violet variety of the mineral zoisite. GIA says it is mined commercially in only one area, the Merelani Hills of Tanzania.
- Violetish blueFine color.
- Blue-violetFine color, more violet.
- Violet-purpleOften chosen when cutting for weight.
- Pale blue-violetLighter stones.
The swatches are illustrations picked to match the color names. Screens and light change how color looks, and a cut stone changes with the light, so judge a stone in person or from a daylight photo.
Which tanzanite color is finest
A deep, saturated violet-blue or blue-violet is the most valuable, and paler hues are more common. GIA's buying guide names a strongly saturated pure blue or violetish blue as the most prized. Cutting for violet-purple wastes less rough than cutting for violetish blue, so cutters weigh a larger violet-purple stone against a smaller, bluer one.
How gemologists describe color
Gemologists describe the color of a stone with hue, tone and saturation, and look at the three together. For colored stones they also look at how evenly the color is spread.
- Hue
- The color you would name, such as blue, green or red, or a blend such as bluish green.
- Tone
- How light or dark that color looks, from pale to very dark.
- Saturation
- How strong or pure the color looks, from dull (grayish or brownish) to vivid.
- Evenness
- How evenly the color is spread through the stone. Color zoning is uneven color, such as bands or patches you can see.
Colored stones have no single color scale like the D to Z scale for diamonds, so sellers use their own words. Ask for a daylight photo and for the size in mm as well as the carat weight.
What affects tanzanite color
- Cause of color
- Vanadium is the likely cause of the blue. Researchers have debated the exact cause.
- Treatments
- Tanzanite is routinely heated to turn a brownish look into blue to purple. GIA says the treatment is stable.
- Light and angle
- Tanzanite is strongly pleochroic: one direction looks blue and another purple, so the way the stone is cut sets the color you see face up.
- Wear and care
- Tanzanite is softer than sapphire and has cleavage, so it suits a protective setting. Strong acids attack it.
Tanzanite color and size
Stones usually need to be large to reach deep, saturated color. Carat is weight, not size. A round 1 carat tanzanite measures about 6.6 mm, against 6.5 mm for a diamond of the same weight. This table gives the face-up size of a well-cut tanzanite.
- 1 ct
- Round: 6.6 mm
- Oval: 8.1 x 5.6 mm
- Cushion: 5.7 x 5.7 mm
- 2 ct
- Round: 8.3 mm
- Oval: 10.2 x 7.0 mm
- Cushion: 7.2 x 7.2 mm
- 3 ct
- Round: 9.5 mm
- Oval: 11.7 x 8.1 mm
- Cushion: 8.2 x 8.2 mm
- 5 ct
- Round: 11.2 mm
- Oval: 13.9 x 9.6 mm
- Cushion: 9.7 x 9.7 mm
- 10 ct
- Round: 14.1 mm
- Oval: 17.5 x 12.0 mm
- Cushion: 12.3 x 12.3 mm
See the full tanzanite size chart for every shape, or use the carat to mm calculator for any weight.
Tanzanite properties
- Hardness (Mohs)
- Value: 6.5 to 7
- Refractive index
- Value: 1.691 to 1.700
- Specific gravity
- Value: 3.30 to 3.38
A blue-violet zoisite. Softer than sapphire, so it suits a protective setting.
How to compare tanzanite stones
- Look at each stone in daylight and under indoor light. Color shifts with the light.
- Ask for the size in mm as well as the carat weight. A tanzanite of the same weight can differ in size by shape and cut.
- Ask whether the color is natural or treated, and ask for the answer in writing.
- For a stone that matters, ask for an independent lab report.
Designing with a colored stone? HeyGema lets you choose the stone shade and renders your design with it.