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TANZANITE

Louis Cauchi Savona
3 days ago
8 min read

Tanzanite is a gem discovered in the 1960’s in the foothills of Africa’s Mt. Kilimanjaro. This gem comes in a variety of shades of blue, violet and purple. The family name is ZIOSITE but the commercial name was given as “Tanzanite” by Tiffany & Company in honour of Tanzania. In fact the name Tanzanite sounds more exotic and appealing than “blue ziosites”.


When one looks from one angle Tanzanites may appear blue, but from another angle they will be purple. What’s more, indoors and outdoors may seem to have different looks. Along with purple and blue, there may be flashes of red, green, yellow, orange or brown. In incandescent light (ordinary lightbulb) tanzanite may look purple and in daylight blue or violet. It is good to note that not all Tanzanites changes colour. However, your final judgement of a tanzanite’s grading ( and also of other gemstones) should be based on its appearance in daylight equivalent light.


Because Tanzanite exhibits 3 colours in gemmological terms it is described as Trichroic (3 colour) gem. Very few gems are trichroic and none display the same three colours as Tanzanite. This makes it very easy to identify Tanzanite from simulants.


In more intense colours, tanzanite may look like sapphire, which costs more. However, sapphire lacks the purplish highlights of tanzanite. Sapphire is a blend of just two colours which are violet blue and greenish blue.


The degree to which light is bent as it passes through a stone is called Refractive index and is measured by a refractometer. In tanzanite the refractive index is 1.691 – 1.700 which is a lot higher than that of ilolite (a simulant of Tanzanite) and lower than that of sapphire ( 1.762-1.770).


These distinctive combination of colours make Tanzanite very difficult to match. Tanzanite is one of the most visually striking gemstones discovered in modern times. Known for its vivid blue-to-violet hues and strong pleochroism (showing different colours from different angles), tanzanite has rapidly become a desired gem in fine jewellery since its introduction in the late 1960s. Although it is a variety of the mineral zoisite, its unique colour and singular geographic source have given it a distinct identity and market value. This article explains tanzanite’s geology, discovery, physical and optical properties, treatments, grading and valuation, market and cultural aspects, ethical concerns, care, and buying guidance.


Discovery and history

Tanzanite was discovered in 1967 in the Merelani Hills near Mount Kilimanjaro in northern Tanzania. Local accounts and popular narratives describe Maasai herders finding unusual blue stones in the region after earthquakes or lightning storms; the exact story varies. Commercial recognition accelerated when gem dealers and prospectors began extracting and marketing the stones in the late 1960s. New York jeweller Tiffany & Co. played a pivotal role in bringing tanzanite to the international market in 1968, coining the name “tanzanite” to highlight its singular country of origin and to give the stone a memorable brand identity.

Tanzanite is a blue-violet variety of zoisite, a calcium aluminium silicate (chemical formula Ca2Al3(SiO4)(Si2O7)O(OH)). Zoisite is an orthorhombic mineral that forms in metamorphic environments. The Merelani deposit formed under regional metamorphism where high temperatures and pressures transformed pre-existing rocks. Trace amounts of certain elements—most importantly vanadium (V3+)—in the crystal lattice are responsible for the vivid blue-violet colour that distinguishes tanzanite from other zoisite.


Uniqueness of origin: Merelani Hills, Tanzania One of tanzanite’s defining market characteristics is its extremely limited primary source—the Merelani Hills in Tanzania’s Manyara Region. Commercially significant gem-quality tanzanite has, to date, only been mined there on any scale. This geographic restriction contributes to the gem’s rarity and long-term interest among collectors and investors.

  • Chemical family: Calcium aluminium hydroxyl silicate (zoisite).

  • Crystal system: Orthorhombic.

  • Colour: Blue, violet-blue, violet, and bluish purple. Natural rough often appears brownish and becomes blue/violet after heat treatment.

  • Pleochroism: Strong trichroic pleochroism—typically showing blue, violet (purple), and reddish-brown or yellow-brown colours along different crystallographic axes. Proper orientation during cutting is crucial to showcase the desirable blue/violet hue.

  • Refractive indices: Approximately nα ~1.69, nβ ~1.69–1.70, nγ ~1.70–1.71 (values can vary slightly by specimen).

  • Birefringence: About 0.008–0.013.

  • Specific gravity: Around 3.35.

  • Hardness: Approximately 6 to 6.5 on the Mohs scale (commonly quoted as about 6.5). This makes tanzanite moderately hard but softer than corundum (sapphire, ruby).

  • Cleavage: Distinct cleavage in one direction, which makes faceting and some jewellery settings more challenging and necessitates care to avoid chipping.

Tanzanite’s spectacular colour is its signature attribute. The gem’s colour varies from violet through blue to purplish-blue, and the exact hue depends on chemical composition (notably vanadium), the orientation of the stone relative to the viewer, and any heat treatment it experienced.


Pleochroism is intense in tanzanite—viewing the stone from different directions changes the apparent colour. Faceters orient the rough so that the dominant face-up colour is the most marketable (usually a rich blue-violet). Because of pleochroism, poorly cut stones or pieces cut from suboptimal rough can appear weak or uneven in colour.


Most gem-quality tanzanite on the market is heat treated, a process generally accepted by the trade. Natural zoisite rough frequently displays brownish or greenish tones; controlled heating in a furnace (typically below 600–700 °C) converts these colours into attractive blue and violet hues by affecting the valence state of elements such as vanadium. Heat treatment is stable and permanent; once heated, the colour will not revert under ordinary conditions.


It’s important for buyers to be told whether a stone has been heat treated—this is standard practice in professional gem trade disclosure. Untreated, vividly blue tanzanite is rare and commands a premium.

The value of a tanzanite gemstone is determined by the same basic factors used for other gems: colour, clarity, cut, and carat weight (the “Four Cs”), plus origin and treatment disclosure. However, emphasis and specifics are specialized for tanzanite:

  • Colour: The most important determinant of value. The finest tanzanites have deep, saturated violet-blue or pure blue tones that resemble certain sapphires. Strong, vivid saturation with good hue balance (not too red/brown or too grey) is highly prized. Very light or brownish pieces are less valuable.

  • Clarity: Eye-clean stones (no visible inclusions) are preferred. Common inclusions include crystals, needles, and growth features. Because tanzanite is often seen in larger sizes with good colour, slightly included stones can still be attractive and valuable if the colour is exceptional.

  • Cut: Cut quality is crucial to show the best colour and minimize the effects of pleochroism. Faceters often choose orientations and shapes (oval, cushion, emerald, and mixed cuts are popular) that maximize colour richness. Well-cut stones return more light and display an even face-up colour.

  • Carat weight: Larger tanzanites are widely available compared to many other coloured gems, so per-carat prices do not escalate as steeply as for rarer stones like larger rubies or emeralds. However, fine-colour larger stones do command premiums.

  • Treatment and origin: Disclosure of heat treatment is standard. The Merelani origin is intrinsic to the identity of the gem and often stated; certification from reputable labs can confirm origin and treatment.


Tanzanite’s attractive colour and relative affordability compared to sapphire have made it popular in rings, earrings, pendants, and bracelets. Its softness relative to corundum means that it’s often set into pieces less exposed to knocks (earrings and pendants) or set with protective settings for rings. Contemporary and vintage jewellery designs both favour tanzanite for its bold, modern colour.

Because tanzanite is not as hard as corundum and has distinct cleavage, proper care is essential:

  • Cleaning: Use warm, soapy water and a soft brush or cloth. Rinse thoroughly and dry with a soft cloth.

  • Avoid: Ultrasonic and steam cleaners are generally not recommended because internal stresses and cleavage could cause fractures. Also avoid exposure to household chemicals and hard knocks.

  • Storage: Keep tanzanite jewellery separate from harder gemstones to avoid scratching. Store wrapped in a soft cloth or in a separate compartment.

  • Regular inspection: Have prongs and settings checked periodically by a jeweller to ensure the stone is secure.


There is limited production of synthetic zoisite (lab-grown) and some simulants can mimic the colour of tanzanite (e.g., coloured glass, synthetic spinel, or synthetic corundum). Because tanzanite’s optical properties—especially pleochroism and refractive indices—are distinctive, a gemmological lab can usually distinguish genuine natural (or natural heated) tanzanite from imitations. Buy from reputable dealers and request written disclosure and certification for higher-value stones.

Tanzanite’s market is shaped by its restricted source, pleasing colour range, and modern provenance. Because high-quality tanzanite is only found in one geographical area, concerns about the longevity of supply and potential depletion attract collectors and investors. However, tanzanite differs from classic investment gems (like top-quality rubies and emeralds) in that it has a shorter market history and greater variability in quality. Collectible value is strongest for stones with intense, saturated colour, excellent clarity, attractive cuts, and larger carat weights.

Tanzanite’s arrival during the latter half of the 20th century and aggressive marketing by major jewellers helped it quickly gain cultural traction.

Many buyers choose tanzanite for its modern, vibrant colour and as an alternative to traditional blue gemstones like sapphire.

Tanzanite mining in the Merelani Hills is primarily artisanal and small-scale mining (ASM), and has been associated with socioeconomic challenges: unstable incomes for miners, variable working conditions, environmental degradation, and occasional land use conflicts. Child labour and unsafe practices have been issues at times, although industry groups, NGOs, and the Tanzanian government have worked to improve working conditions, implement better regulation, and promote traceability.

Several initiatives and companies have attempted to create more ethical supply chains, improve community benefits, and enhance transparency. When buying tanzanite, especially higher-value stones, consumers concerned about ethical sourcing should look for sellers who provide information on origin, supply chain practices, responsible sourcing policies, and third-party certifications or audits.

For high-value tanzanite purchases, consider obtaining a report from an accredited gemmological laboratory (e.g., GIA, AGL, GAGTL or other recognized labs). A lab report can confirm identity, whether heat treatment was applied, and other important optical and physical properties. Some labs may comment on probable origin, though origin determination can be complex and not always definitive.

  • Prioritize colour: Seek stones with strong, well-saturated blue-violet hues; avoid stones with dominant brownish tints.

  • Look for eye-clean clarity in larger stones; small inclusions are common and often acceptable if they do not affect durability or appearance.

  • Ask about heat treatment: Most tanzanite is heat treated and this is acceptable, but disclosure is standard.

  • Request lab reports for high-value purchases to verify identity and treatment.

  • Buy from reputable dealers who provide clear return policies, treatment disclosures, and information about sourcing.

  • Consider settings that protect the stone from knocks and provide some buffer against scratches.

This is a gem which is highly recommended for those with a stressful lifestyle or for those having adrenal fatigue. Tanzanite is a wonderful talisman for anything involving the adrenal glands and thyroid and to strengthen the spine.

Wearing Tanzanite evolves a completely different experience as it channels its energy throughout the body. Its formidable vibes work almost instantly for treating the physical deficiencies as well as detoxifying the entire self. It is said to rejuvenate the body physical and mind from the stress and despairs of life.

This shimmering blue gemstone is a December birthstone and brings the best of benefits for those born under Sagittarius. It is believed to bring good fortune and wealth as well as boosting confidence and self-respect in people.

CONCLUSION

Tanzanite is a modern gemstone success story; it is strikingly beautiful and vivid. Its appeal is based on its unique blue-violet colour, strong pleochroism, and rarity of origin. While most tanzanite on the market is heat treated to develop or enhance colour, the treatment is stable and accepted in the trade. Buyers should pay special attention to colour, cut, and clarity, and be mindful of ethical sourcing and proper care due to the gem’s moderate hardness and cleavage. For those attracted to bold, saturated blues and purples, tanzanite offers an eye-catching, sometimes more affordable alternative to traditional blue gems, with the added appeal of a contemporary backstory and a limited geographic origin.

My advise is to always buy such gemstones from trustworthy and reliable sources.



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