Tanzanite, Alexandrite, and Other Collector Stones

## Beyond the Big Three While ruby, sapphire, and emerald dominate the fine gem market, a constellation of rarer stones commands the attention of serious collectors. These gems — tanzanite, alexandrite, chrysoberyl cat's eye, and others — share a common trait: they are rarer than the Big Three, often display extraordinary optical phenomena, and in some cases come from a single geographic source. ## Tanzanite ### Discovery and Source Tanzanite was unknown to the gem world until 1967, when a Maasai herder named Ali Juuyawatu discovered blue-violet crystals near Merelani, in the foothills of Mount Kilimanjaro, Tanzania. The stones were identified as a variety of the mineral zoisite (calcium aluminum hydroxy sorosilicate) — previously known only as an opaque, uninteresting mineral. Tiffany & Co. recognized the stone's potential, named it "tanzanite" (after its country of origin), and launched it commercially in 1968. It was the most significant new gemstone discovery of the 20th century. Tanzanite comes from a single source: the Merelani Hills in northern Tanzania. The deposit extends along a narrow strip about 7 kilometers long. No other occurrence of gem-quality blue zoisite has been found anywhere on earth. ### Color and Pleochroism Tanzanite displays strong trichroism — three different colors visible along different crystal axes: blue, violet, and burgundy-brown. Most rough tanzanite appears brownish and is heated to 500–700°C to eliminate the brown component and produce the blue-violet color the market demands. The finest tanzanite displays a saturated blue-violet — a color unique among gemstones. GIA describes the best material as "violetish blue" or "bluish violet" depending on the dominant hue. Stones showing strong blue with violet flashes are most valued. ### Market Position Tanzanite occupies a middle tier in the colored stone market. Fine stones of 5–10 carats retail for $500–$1,500 per carat — far below ruby or sapphire but above most commercial colored stones. The single-source nature of tanzanite creates an unusual risk-reward profile: if the Merelani deposit is ever exhausted, existing stones could appreciate dramatically. On the other hand, dependence on a single mine in a developing country introduces geopolitical risk. ## Alexandrite ### The Color-Change Champion Alexandrite is the most famous color-change gemstone. It shifts from green in daylight (or fluorescent light) to red under incandescent light — an effect caused by chromium ions that absorb in a narrow band of the yellow-green spectrum. Daylight, rich in blue-green wavelengths, emphasizes the green transmission. Incandescent light, rich in red wavelengths, emphasizes the red transmission. The quality of the color change — the degree of difference between the two colors and the attractiveness of each color individually — determines value. The finest alexandrites show vivid green in daylight and vivid red in incandescent light with a complete and dramatic change. ### Sources **Russia (Urals)**: The original source, discovered in 1830 in the emerald mines of the Ural Mountains. Russian alexandrites are the standard against which all others are measured — they display the strongest, most attractive color change. However, Russian material is extremely rare; most examples on the market today predate 1900. **Brazil**: Hematita, Minas Gerais. Brazilian alexandrites can display excellent color change, though they typically show a more bluish-green daylight color than Russian material. **Sri Lanka**: Produces alexandrite with good color change, though the daylight color tends toward olive green rather than emerald green. **India**: The Araku Valley in Andhra Pradesh produced alexandrites in the 2000s. Quality varies, but some Indian material rivals Brazilian stones. ### Pricing Fine alexandrite is genuinely rare. Stones over 1 carat with strong, attractive color change command $10,000–$70,000 per carat from Russian origin. Brazilian and Sri Lankan material sells for $5,000–$30,000 per carat for equivalent quality. Alexandrites over 5 carats of fine quality are museum-piece rarities. ## Chrysoberyl Cat's Eye Chrysberyl (BeAl₂O₄) in its chatoyant variety — cat's eye chrysoberyl — displays a sharp, silvery-white line of light across the dome of a cabochon-cut stone. The effect is caused by dense, parallel silk inclusions (needle-like crystals) that reflect light in a single direction. The finest cat's eye chrysoberyl from Sri Lanka shows the "milk and honey" effect: when a point light source illuminates the stone, one side of the chatoyant band appears milky white while the other shows a honey-gold body color. This effect, seen only in the best material, is mesmerizing. Pricing for fine cat's eye chrysoberyl ranges from $1,000–$10,000 per carat for exceptional quality. The effect quality (sharpness, centering, and prominence of the eye) matters as much as body color. ## Other Collector Favorites ### Sphene (Titanite) Sphene displays fire (dispersion) exceeding that of diamond — 0.051 vs. diamond's 0.044. Fine sphene shows flashes of spectral color within a yellow-green to brown body color. The challenge is durability: sphene is only 5–5.5 on Mohs, making it fragile for jewelry. Fine specimens from Brazil, Madagascar, and Pakistan are strictly collector stones. ### Benitoite California's state gem, found only in San Benito County. Benitoite displays a vivid blue color and strong dispersion (fire), fluoresces bright blue under UV, and crystallizes in a crystal system (hexagonal, ditrigonal dipyramidal) so rare that it is the only gem mineral in its class. Stones over 1 carat are rare; over 2 carats is exceptional. A unique American collector stone. ### Grandidierite One of the world's rarest gem minerals, discovered in Madagascar in 1902. Transparent, facetable grandidierite is extraordinarily rare — fewer than a few hundred carats of gem-quality material are known. The color is a distinctive blue-green to teal. Prices for clean stones exceed $20,000 per carat. ### Jeremejevite Another extreme rarity — a colorless to pale blue aluminum borate mineral from Namibia and Madagascar. Faceted stones over 1 carat are exceptional collector pieces. The combination of extreme rarity, attractive pale blue color, and good hardness (6.5–7.5) makes jeremejevite a true connoisseur's gem. ## The Collector's Advantage Collecting rare gems offers several advantages over collecting mainstream stones: - Less competition from retail jewelry buyers keeps prices more rational - Scientific interest adds depth to the collecting experience - Rarity provides stronger long-term appreciation potential - Community of fellow collectors is knowledgeable and engaged The disadvantage is liquidity — rare stones are harder to sell than rubies and sapphires because the buyer pool is smaller. But for collectors who value knowledge and discovery over market liquidity, these stones represent the pinnacle of the hobby.