Rare Gems

Alexandrite is one of the most extraordinary phenomena in the mineral world. Hold it in daylight or fluorescent light and it appears vivid green — sometimes blue-green, sometimes pure green. Bring it into incandescent light or candlelight and it transforms to a rich red or purplish-red. No other gemstone performs this dramatic colour shift, and the quality of the change — how complete and how vivid it is — determines the stone's entire value.

The gem was named after Tsar Alexander II of Russia because it was discovered in the Ural Mountains in 1830, the same year Alexander came of age. The green and red of alexandrite happened to match the colours of the Imperial Russian Guard's uniform — a coincidence that gave the gem immediate prestige in Russia and subsequently across the jewellery world.

Why Does Alexandrite Change Colour?

Alexandrite is a variety of chrysoberyl — the same mineral as cat's eye — coloured by chromium. The chromium in alexandrite creates a very unusual optical situation: it absorbs light in the yellow-green part of the spectrum, transmitting both green wavelengths and red wavelengths simultaneously. In daylight, which is rich in blue and green wavelengths, the eye perceives the stone as green. In incandescent light, which is richer in red and orange wavelengths, the eye perceives the stone as red.

This phenomenon — called metamerism in physics — depends on the chromium concentration and crystal chemistry being precisely right. It is a remarkably narrow set of conditions, which is why alexandrite is so rare and why most chromium-bearing gems do not show the same effect.

Ceylon Alexandrite vs Russian Alexandrite

The Ural Mountain deposits of Russia — which produced the finest alexandrite in the 19th and early 20th centuries — are now essentially exhausted. Russian alexandrite of collector quality is effectively an antique gem category, with stones circulating in the secondary market and commanding enormous premiums for their historical origin and colour quality.

Sri Lanka is now the most important source of natural alexandrite in the world. Ceylon alexandrite differs subtly from Russian material: it tends to be lighter in tone, and the colour change is often described as blue-green to purple-red rather than the pure emerald-green to ruby-red of the finest Russian stones. Whether this is inferior or simply different is a matter of preference — and price. Russian alexandrite with strong colour change commands substantially higher prices than equivalent Ceylon material.

Brazil also produces alexandrite — from deposits in Minas Gerais — and Brazil is now the largest producer by volume. Brazilian stones tend to be lighter in colour than both Russian and Ceylon material and show a less dramatic colour change, though exceptional specimens exist.

How to Evaluate Alexandrite Quality

Strength of colour change is everything. A strong colour change — where the stone appears clearly green in daylight and clearly red under incandescent light — is the most important quality factor. A weak change, where the stone merely shifts from brownish-grey to brownish-purple, is of little value. The ideal is a complete change with vivid, saturated colours in both lighting conditions.

Colour in each light source matters separately. In daylight, you want a pure, vivid green — not yellowish or greyish. Under incandescent light, you want a vivid red or purplish-red — not brownish or dark. Stones that show vivid colour in both lighting conditions are the rarest and most valuable.

Clarity is evaluated normally — eye-clean stones are preferred, though alexandrite at any size above 2 carats is sufficiently rare that some inclusions are accepted. The inclusions in chrysoberyl tend to be distinctive: thin parallel tubes, twinning planes, and fingerprint-like liquid inclusions are characteristic under magnification.

Carat weight affects value dramatically. Alexandrite above 2 carats with strong colour change is genuinely rare. Above 5 carats, it is extraordinary. Most quality Ceylon alexandrite comes to market in sizes under 1 carat.

Gemological Properties

Alexandrite shares its gemological properties with other chrysoberyls: Mohs hardness 8.5 (excellent for jewellery use), refractive index 1.746–1.755, specific gravity 3.73. It is doubly refractive and shows strong pleochroism — three different colours from three different crystal directions. Under a dichroscope, it shows purple-red, orange, and green simultaneously — a striking and diagnostic result that makes identification straightforward.

Alexandrite is not typically treated. Unlike sapphire or ruby, there is no widely practised heat treatment that improves its colour. This means that the majority of alexandrite on the market is in its natural state — a significant advantage from an authentication perspective.

Price Guide and Buying Advice

Alexandrite prices are driven almost entirely by colour change strength:

• Weak colour change Ceylon alexandrite (under 1 ct): USD 500–2,000 per carat
• Good colour change Ceylon alexandrite (1–2 ct): USD 3,000–10,000 per carat
• Strong colour change Ceylon alexandrite (2+ ct): USD 10,000–50,000 per carat
• Fine Russian alexandrite (any size): USD 20,000–150,000+ per carat

Always view alexandrite under both daylight and incandescent light before buying — ideally both at the same time if a split-light viewing tool is available. Request a laboratory report from GRS or Gübelin that explicitly confirms the colour change and origin. Synthetic alexandrite (created by flux or Czochralski methods) exists and is very convincing — laboratory testing is essential for any stone above USD 1,000.

Alexandrite is the gem for collectors who want something genuinely extraordinary — a stone that transforms before your eyes and carries the weight of history in every flash of colour.

Disclaimer: Price ranges are approximate market references. Always consult a certified gemologist before making significant purchases. CeylonGemLuxury does not sell gemstones directly.