Zircon unjustly shares its reputation with the synthetic mineral, cubic zirconia. Zircon happens to be totally natural with the chemical name zirconium(IV) silicate. Zircon has many different colors, most notably blue, and ranges from colorless white to forest green or vibrant orange. The orange variety along with yellow and red were known at “hyacinth” in ancient times because the blue zircon was considered to be a sapphire. Engraving this stone was believed to bestow upon it power to avert lightening for the engraving was considered to be a seal. The popularity of this belief led to reports that no person being struck by lightening wore a hyacinth around his neck.
"If any one is bewitched by phantoms or by magical spells, so that he has lost his wits, take a hot loaf of pure wheaten bread and cut the upper crust in the form of a cross, --not, however, cutting it quite through, --and then pass the stone along the cutting, reciting theses words: 'May God, who cast away all precious stones from the devil after he had broken his commandment, cast away from thee, N., all phantoms and all magic spells and free thee from the pain of this madness.'" --Saint Hidegard, d.1179
According to Albertus Magnus, Pliny placed hyacinth after amethyst as having a similar color but paler. This “fading away” when exposed to sunlight gave the hyacinth its name. On the other hand, Solinus found the hyacinth (zircon) to be blue and watery like a sapphire. The description made by Solinus persisted through the Medieval period. Being of three kinds, the most prized are not red, “granati” meaning “like pomegranate seed”, but blue. The least valuable were those which could not be inscribed. Albertus Magnus says that when hyacinth was worn around the neck, it protected travelers from harm and makes him welcome to hospitality. Zircon, as believed to be hyacinth, was also used to induce sleep since the crystal felt cold. All this being said, zircon was often confused with other gemstones like sapphire and amethyst during the Dark Ages.
Zircon primarily can be found in volcanic rock although it can be found in both sedimentary and metamorphic rocks as well. Large crystals of zircon are considered rare as an accessory crystal. Zircon is about as hard and durable as quartz, both being an attractive substitution for more expensive jewelry especially while away on trips or vacations. Uranium even has been known to be found as an inclusion inside zircon crystals.
Heat treatment may often be use to change the color of zircon crystals. Heat in this way causes brown zircon to be transformed to either colorless white or navy blue. Zircon has few industrial uses, other than its use as the precursor in the process of manufacturing of zirconium dioxide. Sometimes, however, it can also be found in nuclear fuel rods, thus creating irradiated varieties of the crystal as well as heated.
Zircon has been classified as a semi-precious gemstone due to its high refractive index. This being said, zircon is considered a heavy gemstone, but I find this consideration important relative to its size. Zircon can not be eroded by acids while it can lose some of its color in sunlight.The region where zircon is mined has been correlated to a property of its crystal known as birefringence. Gemologist use this property to identify a zircon from its derivative, the cubic zirconium.
Zircon has ben known to imitate synthetic sapphire or spinel, but all three of those crystals reflect differently while under UV light. Spinel will, of course, reflect a red color and zircon will reflect an orange color. Furthermore, radiometric dating of zircon crystals has pinpointed the dates of crystallization to 4.4 billion years ago making them the oldest crystals on Earth.