Zircon

Zircon is not a very well-known gemstone, but it is one of the most important gemstones of today. Many people confuse zircon with the artificial diamond simulant, cubic zirconia. Of course, the two are completely different – cubic zirconia (CZ), is a lab-created synthetic material, while zircon is a naturally occurring gemstone with a very different chemical composition. However, before the introduction of diamond simulants like cubic zirconia and moissanite, white zircon was actually one of the most popular diamond substitutes, owing to its high dispersion and refractive index, and was often marketed under the misleading trade name of ‘Matura diamond’. Zircon is also remarkably dense and exhibits a very pronounced level of birefringence. Zircon has such high birefringence that it may appear fuzzy or display facet-doubling.

Zircon occurs in a wide range of colors, of which white or colorless is likely the least valuable or important. The most popular zircon today is blue zircon, usually occurring with green pleochroism, which can result in interesting teal-like colors. Blue zircon is actually produced by heating more commonly occurring brown zircon. However, only some brown materials have the appropriate physical structure to turn blue when heated, typically only deposits found in South East Asia – which is why most blue zircon comes from Cambodia or Burma. Blue zircon is one of the traditional modern birthstones for December.

Zircon is a tremendously important mineral, indeed its prominence led to the emergence of the discipline of ‘zirconology’ in gemology. It is the oldest mineral on Earth, with samples found in Australia that are over 4.4 billion years old. Scientists discovered that zircon actually contains trace elements of uranium and thorium, both of which are elements with known half-lives. It is the uranium and thorium that cause such tremendous variations in the physical properties of zircon. Zircon is typically classified as low, medium and high zircon, in reference to the presence of optical properties. Low zircon has higher traces of radioactive uranium and thorium, which causes an alteration in physical structure, rendering it near-amorphous, though its physical appearance remains the same as high or medium zircon. Low zircon is typically green to brownish in color. Green zircon is rarely seen in the gem trade and is highly sought after.

Zircon Color

Zircon in its purest form is completely colorless (white), but owing to trace impurities, it can occur in a wide range of interesting colors, including yellow, orange, red, green, blue, violet, brown and combinations in between. Yellow-brown to orange and red zircon are the most common occurrences, along with colorless. Blue is the most popular, but its color is obtained through the heating of brown zircon, usually from Cambodia and Burma. Due to pleochroism, blue zircon can look greenish from certain angles. Medium dark, pure blue stones have the most value. Green zircon is very rare and typically very expensive.

Zircon Clarity and Luster

In general, zircon is transparent to translucent. Impurities cause the various colors. Zircon with cat’s eye chatoyancy is known but very rare. Some crystals contain radioactive elements of thorium and uranium. Over time, the radioactivity breaks down the crystal structure so that such stones tend to a near-amorphous structure, with a slightly lower luster than the crystalline form. These low green zircon specimens are rare and are highly prized by gem collectors. They pose no radioactive heath threat. Zircon exhibits a brilliant, vitreous sheen when polished.

Zircon Cut and Shape

The high birefringence of zircon makes it necessary for the cutter to orient the table of the stone to the optic axis; otherwise the interior may look fuzzy, due to facet image doubling. Colorless stones are most often brilliant cut. Colored stones are most often brilliant or emerald step cut. Round stones are often given a ‘zircon cut’, which is similar to a standard round brilliant cut, but with an extra row of facets at the edges. The most popular shapes include ovals, rounds, pears, octagons (emeralds) and fancy trillions. Small melees are also popular.

Zircon Jewelry

Zircon is brittle and therefore is sensitive to knocks and pressure. However, it has good hardness and durability. The gem has the tendency to wear along facet edges owing to its brittle tenacity, so its use in zircon rings, should be limited to protective style settings or occasional wear jewelry. Most zircon stones are small in size, due to their dense nature, but some rare large stones can be found. Larger stones are excellent for bold designs, such as unique pendants or brooches. Blue zircon is very popular for rings and earrings, and colorless zircon is often used in bridal jewelry as a diamond substitute.

Source: Gem Select