Zircon is a naturally occurring mineral composed of zirconium silicate (ZrSiO4), distinct from the synthetic, lab-created material known as cubic zirconia (ZrO2). Dating back over four billion years, it is one of the oldest minerals on Earth. While zircon is found globally, gem-quality material is rare and occurs in a wide spectrum of colors, including yellow, red, green, and the common brownish-red. The highly sought-after blue color is seldom found in nature and is typically the result of a precise modification process.
Primary Sources of Zircon Material
The global supply of gem-quality zircon, particularly the material that can be successfully treated to an electric blue color, is highly concentrated geographically. Southeast Asia is the most significant source, yielding the high-clarity rough necessary for blue conversion. Cambodia stands out as the premier source, particularly the deposits found in the Ratanakiri Province. The zircon from this region possesses the ideal trace element composition required to achieve the most vibrant blue hues upon treatment.
Neighboring countries, including Vietnam and Thailand, also produce commercial quantities of zircon rough, often recovered as a byproduct of corundum mining. Other notable locations that yield gem-quality zircon include Sri Lanka, which is known for a variety of colors, and certain areas in Myanmar and Madagascar. Australia also produces large volumes of zircon, though much of this material is utilized for industrial applications rather than the gemstone trade.
Geological Environments Where Zircon Forms
Zircon forms primarily as an accessory mineral in the cooling process of magmatic rock, most often crystallizing within silica-rich igneous rocks like granite and syenite. During crystallization, zirconium, silicon, and oxygen combine to create the dense, tetragonal crystals. Because of its exceptional chemical stability and hardness, zircon is highly resistant to both mechanical weathering and chemical alteration.
Once the host igneous rock is exposed and begins to weather, the durable zircon crystals are released from the rock matrix. These released grains are then transported by water and concentrated in secondary sedimentary environments due to their high density. This process leads to the formation of alluvial deposits, often referred to as gem gravels or placer deposits, which are the most common source for commercially mined gem-quality material.
How Zircon Becomes Blue
The typical natural color of zircon rough is brown or reddish-brown, which results from minor structural damage within the crystal lattice. This damage, known as metamictization, is caused by the internal radioactive decay of trace elements like uranium and thorium incorporated during the crystal’s formation. The process of creating blue zircon involves restoring the crystal structure and modifying the color centers through controlled heat treatment.
To achieve the stable blue color, the brown or reddish-brown zircon must be heated to temperatures ranging from 900°C to 1000°C. The heating is performed in a reducing atmosphere, meaning the environment within the furnace is intentionally deprived of oxygen. This oxygen-deprived environment changes the oxidation states of certain trace elements within the crystal. Not all brown zircon will respond to this treatment; only material with the correct trace element profile can successfully be converted to the prized blue color. The resulting blue color is generally stable, although prolonged exposure to ultraviolet light or additional heat can occasionally cause the color to revert to its original brown or a colorless state.