Natural alexandrite is only found in a few locations worldwide and mining yields are very low, making natural stones scarce, small in size, and extremely expensive. For these reasons, most of the alexandrite jewelry on the market today is made with lab created stones. But how exactly are these synthetic gems created in a lab?
The most common method for producing synthetic alexandrite is the flux process. This technique involves heating a mixture of aluminum oxide, beryllium oxide, silicon dioxide, and trace elements like chromium, iron, and titanium. These substances are combined with lithium molybdate and lithium vanadate fluxes which aid in melting and dissolving the raw materials. The fluxes allow the mixture to melt at a lower temperature between 1300-1600°C compared to the 2050°C melting point of natural alexandrite. The raw materials and fluxes are placed in a platinum crucible within an electrical furnace to melt them together.
As the melt cools, alexandrite crystals begin to form. To encourage larger crystal formation, a seed crystal of synthetic alexandrite may be dipped into the molten material. The melt is then allowed to cool very slowly over the course of several days to weeks. This slow cooling enables the proper chemical structure to form and allows large single crystals to grow on the seed.
After crystallization is complete, the solid flux material must be removed to extract the lab created alexandrite gems. This is done by submerging the growth in hot water or acid baths which dissolve away the flux while leaving the alexandrite intact. The synthetic crystals are then cut and polished into faceted stones that can be set into jewelry.
While the flux method produces fine gemstones, it can result in inclusions within the alexandrite. Some manufacturers utilize an alternate technique called the Czochralski process to grow higher clarity synthetic alexandrite crystals. This method suspends a seed crystal in molten raw materials and rotates and draws it upwards as single crystal growth occurs on the seed. The resulting lab created alexandrite often has fewer inclusions than stones produced through the flux method.
Regardless of the specific production technique, the essential process of "growing" synthetic alexandrite crystals involves dissolving and recrystallizing aluminum oxide and trace elements at high temperatures. Skilled growers carefully control conditions like heat and cooling to foster the development of lab created gems with crystal structures and chemical compositions that mimic natural alexandrite's color-changing properties and durability. Today's lab-made alexandrite provides an affordable alternative to extremely rare natural stones.
