Zircon: meaning, properties and lore

The mineral

Zircon is the most significant ore of the element zirconium and the most important ore of the rare element hafnium. Lead can appear in it only as a byproduct of the radioactive decay chains of thorium and uranium.¹²

Zircon's Mohs hardness ranges from 6 to 7.5, and its specific gravity ranges from 3.90 to 4.73. Its high refractive index falls between 1.925 and 1.984, with a tolerance of plus or minus 0.040. Its birefringence ranges from 0.000 to 0.059, and the stone weighs more than most gems of like size.³⁴²

Zircon is transparent to opaque and has a conchoidal to uneven fracture and a brittle tenacity. It has fair to good toughness, but it can be brittle. Because of its weight, it feels heavier in the hand than most gems of similar size.¹⁴³

Most zircon crystals are dark brown to black because of iron oxide impurities. The mineral occurs in yellow, green, red, reddish brown and blue hues, and the GemKids account lists blue, green and autumn colours such as cinnamon, sherry, yellow, orange and red. Colorless and cat's-eye zircons also exist.¹³⁶⁷

Zircon often takes up traces of uranium and thorium, because their cation sizes are close to zirconium and they can substitute in the lattice. Radioactive decay damages the crystal structure until it is nearly amorphous, a process called metamictization. Gemologists class zircon as low (metamict), intermediate or high according to the degree of this radiation-caused damage.¹³⁵

Zircon is most often found in igneous environments, usually in granite pegmatites and nepheline syenite pegmatites, and also in high-grade metamorphic rocks and placer deposits. Notable localities include Mogok in Burma (Myanmar), where transparent gemmy green and brown zircon comes from, and Store Kufjord on Seiland Island in Norway, known for transparent dark red crystals. Zircon found in Australia is about 4.4 billion years old, which makes it the oldest mineral on earth.¹³⁷

History and lore

Many scholars think the name zircon comes from the Arabic word zarkun, meaning cinnabar or vermilion. The two accounts differ, and the Arabic origin is the one most scholars favour.⁸⁷

Zircon's optical properties are close enough to those of diamond to account for centuries of confusion between the two gems. Colourless zircon was widely used as a diamond simulant in the early 1900s, before being replaced by more convincing look-alikes. Its sparkle and flashes are diamond-like, which is why the two were confused for so long.³⁸⁷

In the Middle Ages, zircon was thought to induce sound sleep, drive away evil spirits, and promote riches, honor, and wisdom, according to the Gemological Institute of America's account of medieval belief.⁸

Blue zircon was a particular favourite in Victorian times, when fine gems were often featured in English estate jewellery dating from the 1880s. George Kunz, Tiffany's gem buyer, was a notable zircon advocate who once proposed the name starlite to promote the gem's fiery nature.⁸

In September 2011, GIA examined two zircons from central Australia that turned orange in darkness and faded to near colorless in light, as reported by S.F. McClure in Gems & Gemology. Tenebrescence, the reversible photochromism seen in gemstones such as hackmanite, is unusual in zircon.²

Woodhead's 1991 study in American Mineralogist described the metamictization of zircon and its radiation dose-dependent structural characteristics. Skilful lapidaries often made imitation diamonds of zircon, ruby, cat's-eye, rock-crystal and glass, so such gems should be tested with the aid of learned experts.⁵⁹

Birthstone and other links

Zircon is a birthstone for the month of December, along with turquoise and tanzanite, according to the Gemological Institute of America.³⁸

What crystal practitioners say

Zircon's supposed meaning, as described by its modern users, centres on calm, clear thinking and a sense of abundance. Their view is a present-day one and is not drawn from old writings.

Practitioners say zircon is a stone of inner peace and focus. Crystal practitioners use it in meditation to settle the mind. The stone is said to support prosperity in the home and in work.

Believers in crystal work associate zircon with the home, prosperity and clarity. Practitioners wear it or keep it near the workplace. Crystal healers say the stone brings a sense of order to a room.

Crystal healers say zircon is used for cleansing and charging by practitioners. Users of crystal work keep the stone with other gems. Practitioners place it on a clean surface between uses.

What testing has found

Researchers at Gems & Gemology tested zircon and recorded its optical behaviour under ultraviolet light and in the dark. A 13.16 ct reddish orange zircon darkened to brown after short-wave UV exposure, and the darkening was reversible when stored in the dark. The darkening was much faster than the recovery, and the colour returned within the first 10 to 20 hours of storage at room temperature. These tests measured the stone's colour change, and they did not test any claim about the wellbeing of a person.²

Raman and FTIR spectroscopy show that low (metamict) zircon has peak loss, peak broadening, and an undefined baseline compared with high zircon. Trace-element chemistry combined with spectroscopy may help detect heat treatment in some types of zircon. These are laboratory findings on the stone, and they do not test any claim made by crystal healers.⁵