Although the blue color of zircon is brought out by heat,
it possessed a characteristic brightness and softness.
Beautiful blue zircon gained popularity after its sudden appearance on the world market in the 1920s. The blue zircon ring in the photograph below is a piece from that period. In Thailand, brown zircons were packed in charcoal and heated, making it possible to change them to a blue color not seen before.

Since the late 18th century, colorless and very light yellow zircons have been mined in Matara, located in the south of the island of Sri Lanka (formerly Ceylon). There were called "Matara diamonds," in reference to the low-quality diamonds they resembled. In Precious Stones (1896), Max Bauer wrote that transparent yellowish-red zircons were called "hyacinth," though they were not popular. At the time, almost all zircons were being mined from the alluvial deposits of Ceylon along with spinel, sapphire, and cat's-eye chrysoberyl. A gem that occurs in many colors, zircon's current major source is Sri Lanka, followed by Cambodia and Thailand.

Zircon is strongly doubly refractive, meaning that light entering it is split into two beams. Looking at the photograph to the next page, one can notice how the facet junctions seen on the far side through the gemstone are doubled, appearing as two lines. This effect is about twice as strong in zircon as it is in peridot.
The doubling effect is more pronounced in thicker stones, but it depends on the direction of observation. The presence of such doubling can assist in the separation of singly refractive gemstones, which do not split light, from doubly refractive gems. Furthermore, the degree of doubling seen under magnification can be used as a reference in distinguishing between various doubly refractive gemstones.

Blue zircon's color will fade to about half its overall depth when exposed to direct sunlight for an hour or so. If kept in a dark place such as a safe, however, its blue color will return. The day after its exposure to sunlight, the color will still be about 10 to 20 percent faded, but within a few days its original beautiful color will be fully restored.

Blue zircon is slightly harder than quartz at 7 but chips easily, so durability must be considered when using it in a ring. This gemstone will maintain its beauty longer when set in a pendant or brooch, where it is less likely to be damaged.
Ring, Platinum
Blue Zircon 1pc
Possibly Untreated
Privately Owned Piece,
circa 1920