Alexandrite: The Enchantment of a Legendary Color-Changing Gemstone

“Emerald by day, ruby by night” is the metaphor used to describe the charm of alexandrite, a color-changing gemstone in the chrysoberyl mineral group that can reveal green to bluish-green colors under daylight-equivalent light before displaying red to purplish-red colors under incandescent light. The beauty of a single gemstone thus offers another shade to discover when the light source changes, with both the specific color shades and the prominence of the color change varying from stone to stone.

Mineralogically, alexandrite has the chemical formula BeAl₂O₄, with chromium (Cr³⁺) serving as the key element responsible for the color and color-change phenomenon of this gemstone.

(Note: Information regarding meanings and beliefs is based on historical and cultural records and does not represent scientifically proven properties.)

Value Accumulated Through History

Alexandrite is known for its discovery during the 1830s in the Ural Mountains of Russia. Gemstones from these early deposits displayed green and red hues, matching the military colors of the Russian Empire at the time. The name "Alexandrite" was given to honor Alexander II, who was then the heir apparent and later ascended the throne as Emperor of Russia. The story of this gemstone has thus been tied to Russian history ever since its discovery.

Beyond its namesake heritage, rarity is a major driver of natural alexandrite's value, particularly for stones exhibiting fine color and a prominent color change. Most faceted stones weigh under 1 carat; thus, finding large stones with high color quality is exceptionally rare. Traits that are especially admired include a distinct shift from bluish-green under daylight-equivalent light to red or purplish-red under incandescent light, combined with good color saturation and clarity.

A notable gem example is the “Whitney Alexandrite,” weighing 17.08 carats, from the Hematita mine in Minas Gerais, Brazil, which Coralyn Wright Whitney presented to the National Museum of Natural History, Smithsonian Institution, in 2009. This stone is recorded for its exceptional size, clarity, and color change, displaying a raspberry color under incandescent light and a teal color under daylight.

Why Alexandrite Changes Color

• Color Change Phenomenon Mechanism

  The color-change phenomenon in alexandrite results from the light absorption behavior of color-causing elements within its crystal structure—specifically chromium (Cr³⁺)—combined with spectral differences across various light sources. As light passes through the gemstone, certain wavelength ranges are absorbed. The remaining light transmitted to the eye causes us to perceive different colors when the light source changes.

  Alexandrite may display green to bluish-green under daylight-equivalent light and red to purplish-red under incandescent light, with both color shades and the prominence of the change differing among individual stones. - Distinction Between Color Change and Pleochroism

  In addition to color change caused by different light sources, alexandrite also exhibits pleochroism, which is the appearance of different colors when light travels through the crystal in different directions.

  These two optical properties have distinct causes: color change involves changing the external light source, whereas pleochroism relates to the direction light travels through the crystal matrix. Faceting also directs light through the gemstone in multiple directions, so the color observed from the face-up view may result from a combination of these pleochroic colors.

Evaluating Color and Color Change

• Color Under Different Light Sources: Evaluate hue, tone (lightness-darkness), and saturation under both daylight-equivalent light and incandescent light to observe the gemstone's appearance under both lighting environments.
• Prominence of Color Change: Evaluate the degree of contrast between both lighting conditions, alongside face-up color coverage, clarity, and cut quality, without assuming that every stone must undergo an identical or equally dramatic shift between the same color pair.

Shapes, Cutting, and Design

• Planning and Pre-cutting Considerations: Because alexandrite is a rare and precious gemstone, lapidaries must carefully analyze the rough crystal shape, inclusions or internal characteristics, pleochroic direction, and color behavior under different light sources. This information guides the cutting strategy to ensure color and brilliance are prominently displayed from the face-up view while retaining as much weight as appropriate for each rough piece.
• Common Cutting Styles
  • Mixed Cut: The most common cutting style for alexandrite, combining a brilliant cut on the crown with a step cut on the pavilion. Common shapes include oval and cushion. Shape selection and proportions are determined in combination with the rough gemstone's color and physical characteristics.
  • Cabochon Cut: Used for stones containing slender, parallel inclusions aligned in proper directions that exhibit chatoyancy (cat’s-eye effect). The gemstone is shaped into a smooth-domed cabochon and oriented so the light eye spans across the surface. This group is known as Cat’s-eye Alexandrite, displaying both chatoyancy and color change within the same stone.

Major Sources

• Russia — Ural Mountains: The historical source tied to the discovery and naming of alexandrite.
• Brazil — Lavra de Hematita: Located in Minas Gerais state, a deposit with recorded discoveries in 1987 that played a significant role in Brazil's alexandrite production history.
• Sri Lanka (formerly Ceylon): Another documented origin for alexandrite, where it is recovered from gemstone alluvial deposits.
• India, Tanzania, and Madagascar: Alexandrite has also been reported from these countries, with color traits and internal features varying among individual stones.

Internal Features and Inclusions

Internal features that may be encountered include mineral crystal inclusions, needles or silk, particle clouds, and fluid inclusions arranged in fingerprint-like patterns (fingerprints). The types and distribution of inclusions vary from stone to stone.

When slender inclusions are parallel and properly aligned, certain alexandrite stones can display a cat's-eye effect alongside color change. Internal characteristics also provide supportive data for gemstone identification, evaluated together with optical properties and chemical composition.

Quality Enhancement and Durability

Generally, alexandrite is a gemstone that is untreated, making quality enhancements uncommon for this species.

However, some stones may undergo fracture filling to improve visual clarity, which should be clearly disclosed. If a gemological laboratory report is available, the specific enhancement details noted for that gemstone can be reviewed accordingly.

Durability and Wearability: Alexandrite has a hardness of 8.5 on the Mohs scale, excellent toughness, and no cleavage, making it exceptionally well-suited for various types of daily-wear jewelry, including rings.