Natural Tanzanite

Tanzanite is one of the most fascinating gemstones discovered in the 20th century (1967). A thousand times rarer than diamonds, it is found in only one place in the world. Its color, ranging from sapphire blue to deep purple, makes it a prestigious stone, made famous by Tiffany & Co.

1. Identity and Physical Properties

Tanzanite is the blue variety of the mineral species Zoisite .

• Hardness: 6.5 to 7 on the Mohs scale . It is more delicate than sapphire. It is perfectly suited for cocktail rings, pendants, and earrings, but requires a protective setting for everyday wear.

• Crystalline system: Orthorhombic. It is famous for its exceptional trichroism : it displays three different colors (blue, violet and burgundy) depending on the axis from which it is viewed.

• Composition: Aluminum and calcium silicate containing traces of vanadium , responsible for its color.

2. The Colour Palette: What value?

The value of tanzanite is dictated by the depth of its color.

The “Deep Royal Blue” / “Vivid Violet”

• Description: A saturated, intense color, where blue and purple blend together without any shade appearing washed out.

• Value: The darker and more saturated the stone, the higher its price per carat. Small stones are often light; intense colors are generally found above 3-5 carats.

“Peacock” or “Fancy” Tanzanite

• Description: Natural shades of green, yellow or pink (often unheated).

• Trend: Highly sought after by collectors for their atypical and organic appearance.

3. Quality Criteria (The 4Cs of Tanzanite)

The Size (Cut)

The size is crucial in determining the pleochroism. An expert cutter will choose to favor either the "Blue dominant" side (more expensive, as it resembles sapphire), or the "Violet dominant" side (more electric and typical).

Clarity

Tanzanite is generally considered a "clean" stone. At Dodeca Diamonds , we require "eye-clean" stones . Visible inclusions are rare and significantly devalue the gem.

The Treatment - THE STANDARD

• Heating (H): Unlike sapphire, where heating is optional, 95% of tanzanites are heated at a low temperature (approx. 500°C) to transform their natural brown tones into vibrant blue/violet. This treatment is stable, permanent, and universally accepted.

• Unheated: Extremely rare. These stones often display "petrol" or bicolor green-blue reflections.

4. Investment and the Market

The main investment argument is the "end of life" of the mines . The Merelani deposit is estimated to be exhausted within the next 15 to 20 years. It is often called "the stone of a generation": those who buy today own a resource that will no longer be extracted tomorrow.

The "Dodeca Diamonds" council: "Tanzanite is the stone of visual love at first sight. For an investment, look for stones that display red flashes within the blue when moved under warm light. This is a sign of exceptional saturation. While diamonds are found on several continents, all the tanzanite in the world comes from a strip of land only 4 km long in Tanzania."

Geographical Origins: The Signature of the Terroir

The origin of a tanzanite is not just a mention on a certificate; it is a guarantee of specific "colour" and rarity.

1. Tanzania (Merelani Hills): This is the only deposit in the world, located at the foot of Kilimanjaro. No other source has ever been discovered, giving this stone a unique and distinct geological character.

II. A Closer Look at Trichoism

That's the "magic" of tanzanite.

• The phenomenon: A raw tanzanite crystal is naturally blue, purple, and burgundy.

• Observation: Even a cut stone changes its appearance depending on the lighting. In daylight, it will appear bluer; under artificial light (evening), it will reveal its violet and raspberry hues. It is the ultimate chameleon stone.

III. Light Analysis: The "Velvet" Glow

Tanzanite has a unique ability to absorb and redistribute light, creating a softer, more "velvety" glow than sapphire, while still remaining extremely brilliant.

IV. Dodeca Diamonds Buying Guide

1. Saturation: Avoid overly light-colored stones (pale lilac), which are very common. Aim for "AAA" (a commercial term for maximum saturation).

2. Examining the cylinder head: Check for scratches, as tanzanite is softer than corundum.

3. Certificate: Although less prone to synthetics, a laboratory certificate is essential to confirm the nature of the gem and the absence of surface treatments (coating).

“The Maasai tell the story of how a bushfire caused by lightning transformed the brown stones of the soil into sparkling blue crystals. This is how tanzanite was born. At Dodeca Diamonds , we see this stone as an inheritance: buying a tanzanite today means acquiring a piece of a geological treasure whose source is running out. It is the meeting of absolute rarity and a color that nature has bestowed upon only one people, in one place.”