How to Evaluate Tanzanite Quality: Trichroism, Color Zoning & Clarity
Tanzanite quality is judged first on color: the most valued stones show a deep, saturated violet-blue to blue-violet of medium-dark tone. Tanzanite is strongly trichroic, showing blue, violet, and brownish tones from different directions, so how the cutter orients the stone is itself a quality factor. Almost all tanzanite is heat-treated to bring out the blue-violet, which is standard and accepted; the treatment to watch for is surface coating. Found in only one place on earth, tanzanite is prized for its rarity as much as its color.
Tanzanite is the blue-violet variety of the mineral zoisite, and it has a history measured in decades rather than centuries: it was discovered in 1967 near Mount Kilimanjaro and named by the jeweler Tiffany after Tanzania, the only place on earth it is found. That single, finite source is central to how the stone is valued. Tanzanite is also the modern December birthstone, prized for a color that can rival fine sapphire.
What makes tanzanite unusual to evaluate is trichroism: the same stone shows three different colors depending on the direction you view it through. Cutting it well means choosing which of those colors to favor, which makes orientation a genuine quality factor alongside color itself. This guide leads with color, then explains how trichroism, clarity, and treatment shape what a tanzanite is worth.
6.5-7
Mohs hardness
December
Birthstone
Tanzania
Sole source
Trichroic
Three colors
Why Color Comes First in a Tanzanite
Color in a tanzanite is read through hue, saturation, and tone. The most valued hue is a violet-blue to blue-violet, with the finest stones showing a pure, saturated blue close to a fine sapphire, lifted by violet flashes. Saturation is the strength of that color, and it is what separates a remarkable tanzanite from a pale one. Tone sits ideally in the medium to medium-dark range. Too light and the stone looks weak and greyish; too dark and it loses life. Larger tanzanites tend to show richer color, because depth of stone deepens the color, so small stones often appear paler.
Top color is sometimes described in the trade with grades such as exceptional or vivid, but the eye is the real judge: a deep, lively violet-blue with no grey or brown cast is what commands the premium. For where tanzanite sits as the December birthstone and among the colored stones generally, the birthstone guide covers each one. Because its best color resembles fine blue sapphire, tanzanite is often weighed against it; sapphire follows the same color-first logic, set out in how to evaluate sapphire quality.
Trichroism and Why the Cut Matters So Much
Tanzanite is strongly trichroic, which means a single crystal shows three different colors along its three axes: typically blue, violet or purple, and a brownish or burgundy tone. This is not a flaw; it is a property the cutter has to manage. Orienting the finished stone to show the most blue gives the most valuable result, but it often means cutting against the longest direction of the rough and losing more weight. Orienting to keep weight can leave more violet or a hint of brown. So the cut of a tanzanite is a decision about color as much as about sparkle.
On top of that color choice, the cut is judged the same way as any colored stone: even color face-up, no pale window through the center, and proportions that are not so deep they darken the stone. Tanzanite can also show color zoning, uneven patches of blue and violet, which a skilled cutter works to minimize. When you compare two tanzanites of similar color, the one that reads as a cleaner, more even blue-violet has usually been cut with more skill and sacrifice.
Clarity and the Single Source
Fine tanzanite is usually eye-clean, with no inclusions visible without magnification, so clarity is more of a baseline expectation than a point of comparison. Eye-visible inclusions, especially any that threaten the stone's durability, lower value and are a reason to keep looking. Because tanzanite has one direction of easy cleavage, internal fractures matter for soundness as well as appearance.
Origin works differently for tanzanite than for almost any other gem. It comes from a single small area in the Merelani Hills of Tanzania and nowhere else, so origin is not a premium to compare between sources; it is the whole story. That single, finite supply is a large part of why tanzanite is valued, and it is why the stone is sometimes described as rarer than the classic gems whose deposits are spread across many countries.
Treatment and Honest Disclosure
Nearly all tanzanite is heat-treated, and this is so routine that it is effectively assumed. Most rough comes out of the ground a brownish or yellowish color, and gentle heating, often at modest temperatures, removes the brown and brings out the blue-violet the stone is prized for. The treatment is stable, permanent, and entirely accepted; genuinely unheated tanzanite that shows good color is rare. Heating is not a mark against a tanzanite and does not need to lower a buyer's confidence.
The treatment to watch for is surface coating. A thin coating is occasionally applied to deepen or improve color, and unlike heat it is not durable; it can wear or scratch off and is not always disclosed. A reputable seller states that a stone is heat-treated, as expected, and discloses any coating clearly. For what genuine means and the disclosure to expect from any seller, see your jewelry questions answered.
Disclosure and Care Note
Heat treatment is standard for tanzanite and not a concern; ask instead whether a stone is coated, which is less durable. For care, tanzanite is relatively soft with one direction of cleavage, so avoid ultrasonic and steam cleaners and hard knocks; clean gently with warm soapy water, and favor protective settings for rings.
In Short
1Color leads: a deep, saturated violet-blue of medium-dark tone, with no grey or brown, is the goal.
2Trichroism makes the cut a color decision; a well-oriented stone shows blue-violet rather than brown.
3Heat treatment is standard and fine; watch for coatings, and wear tanzanite gently because it is soft.
Tanzanite Quality Quick Reference
A one-page reference covering the violet-blue color range to look for, how trichroism affects cut and color, the heat and coating disclosures to ask about, and the care a softer stone needs.
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Tanzanite rates about 6.5 to 7 on the Mohs scale and has one direction of easy cleavage, which makes it noticeably softer and more fragile than the corundum and beryl gems. It is a beautiful choice for earrings and pendants, and works in rings with a protective setting and careful wear, but it is not a stone to treat carelessly. The quality that decides what a tanzanite is worth comes down to color first, then the orientation and cut that trichroism demands, with clarity and treatment refining the picture and a single, finite source underpinning its rarity. A buyer who learns to read color and understands trichroism can choose a tanzanite with real confidence. For the wider framework of evaluating any fine piece, the fine jewelry buying guide covers what to check and what to ask. Among the purple-leaning stones, tanzanite sits alongside the more affordable amethyst, which trades rarity for everyday value. Every order ships free with a 30-day return policy.
Frequently Asked Questions
01
What is tanzanite?
Tanzanite is the blue-violet variety of the mineral zoisite, discovered in 1967 and found only near Mount Kilimanjaro in Tanzania. It was named by the jeweler Tiffany after its country of origin and is the modern December birthstone. Tanzanite rates about 6.5 to 7 on the Mohs scale, softer than the major gems, and is prized for a violet-blue color that can rival fine sapphire.
02
What is the most important factor in tanzanite quality?
Color is the most important factor in tanzanite quality. The most valued stones show a deep, saturated violet-blue to blue-violet of medium-dark tone, with no grey or brown cast dulling the color. A smaller tanzanite with rich color is worth more per carat than a larger, paler one, and larger stones generally show deeper color because depth of stone intensifies the blue-violet.
03
Why does tanzanite show different colors from different angles?
Tanzanite is strongly trichroic, meaning it shows three colors along its three crystal directions: typically blue, violet, and a brownish tone. This is a natural property of the stone, not a flaw. The cutter decides which color the finished gem favors, and orienting it to show the most blue-violet, rather than cutting to save weight, produces the most valuable result. Trichroism is why cut and orientation matter so much for tanzanite.
04
Is tanzanite rare?
Tanzanite is genuinely rare because it comes from a single small area in Tanzania and nowhere else on earth. That finite supply, which is expected to be exhausted within decades, is a major part of its appeal and is why it is sometimes described as far rarer than the classic gems, whose deposits are spread across many countries. Rarity, alongside color, is central to what gives tanzanite its value.
05
Are tanzanites expensive or valuable?
Tanzanite value is driven by color and size, lifted by its single-source rarity. Pale or small stones are quite accessible, while large stones with deep, saturated violet-blue color command strong prices. Value rises sharply with richer color and larger size, so a vivid medium-dark stone is worth far more than a pale one of the same weight. Its rarity gives it a value floor that more abundant colored stones lack.
06
Is tanzanite always heat-treated?
Nearly all tanzanite is heat-treated, and the treatment is standard and accepted. Most rough is brownish or yellowish, and gentle heating removes the brown to reveal the blue-violet the stone is known for. The treatment is stable and permanent, and a genuinely unheated tanzanite with good color is rare. The treatment to ask about instead is surface coating, which is less durable and should always be disclosed.
07
Can tanzanite be worn every day?
Tanzanite needs more care than most gems for daily wear. At about 6.5 to 7 on the Mohs scale, with one direction of easy cleavage, it can scratch and is vulnerable to a sharp knock. It is an excellent choice for earrings and pendants, which see less impact, and works in rings with a protective setting and mindful wear. Avoid ultrasonic and steam cleaners, and clean it gently with warm soapy water.
