Zircon

Zircon, traditionally considered as ‘semi-precious’, is a fine natural gemstone with a sub-adamantine lustre and a high dispersion (also called ‘fire’). Zircon comes in a wide range of colours including yellow, brown, orange, red, violet, blue, and green. 

Zircon can also be colourless and when it is it can easily be mistaken for diamond. It is important not to confuse zircon with cubic zirconia (CZ), which is sometimes referred to as ‘zircon’. CZ is a man-made product that resembles natural zircon and diamond with high lustre and dispersion. CZ is used as an inexpensive alternative to diamond in jewellery.

Zircon contains small amounts of radioactive elements that can, over time, alter its crystalline structure producing what is called metamict or ‘low’ zircon. When this occurs the physical and optical properties become different from those of ‘high’ zircon. The radioactive elements present in zircon do not make it radioactive and it poses no threat when worn in jewellery. The descriptions and details provided in this text refer to ‘high’ zircons.

Where can you find the zircon you need?

Pierres de Charmes carries a vast selection of fine quality zircons. Our collection of well-cut stones includes many different shapes and sizes including calibrated stones and melee parcels in different colours.

Zircon Fact Sheet

Zircon is valued for its high dispersion and bright vitreous to sub-adamantine lustre. It is usually cut to maximize brilliance and fire. Zircon has a hardness of 6.5 – 7.5 on the Mohs scale and has a low to moderate toughness.

There are many tools and observations gemmologists and appraisers can use to identify zircon. It is however impossible to take a refractive index reading because zircon has a refractive index that is over the limit of standard refractometers. Zircon’s high birefringence means that a doubling effect of inclusions and facet junctions can be seen with a loupe or microscope. Zircon has a relatively high density, which can be helpful as it will feel heavier than some other gems and gemmologists can measure the specific gravity to confirm the identity. Due to the uranium in its structure, zircon has a diagnostic absorption spectrum that can be seen with a spectroscope.

Rough zircon crystals are square or rectangular tetragonal prisms often terminated with pyramids. They may also be found as water-worn pebbles. Zircon’s high lustre is obvious even in the rough state.

Producing Countries

Major zircon deposits are found in Myanmar, Cambodia, Sri Lanka, and Thailand. Deposits are also found in Brazil, Korea, Mozambique, Nigeria, Tanzania, Vietnam, and France. Zircon is found predominantly in secondary, often alluvial, gem gravels.

Is zircon treated?

Heat is the most common treatment for zircon. Many brownish-red zircons are heated to produce blue, golden yellow, or colourless stones. Heat treatments can also reverse the internal destruction caused by radioactive elements transforming a ‘low’ zircon into a ‘high’ zircon. It should be noted that although many are treated in a lab some zircons can be altered by heat in their natural geological environments.

Zircon in Jewellery

Zircon’s high lustre and dispersion have made it a popular choice in jewellery. Zircon chips fairly easily and has a moderate hardness which makes it best suited for earrings or pendants. It can be set in rings where the setting style offers some protection for the stone and clients should be careful to avoid hard surfaces or sharp impacts.

Zircon is the birthstone for the month of December.

Value and Quality Criteria

Size, colour saturation, and clarity are the main quality criteria for zircon. The quality of the cut will have a major impact on the appearance and value of the stone.

Fun Fact

A zircon found in Australia is considered to be the oldest known mineral on the planet with an age of 4.4 billion years.

Schumann, W. (2000). Guide des pierres précieuses: Pierres fines et ornementales. Lausanne: Delachaux et Niestlé. p.108 

Zir-2. In Cours de base en gemmologie Gem-A. London, 2010 

Gem property Chart A [Chart]. (n.d.). In Gemological Institute of America (GIA). 1992

Zir-1. In Cours de base en gemmologie Gem-A. London, 2010 

Schumann, W. (2000). Guide des pierres précieuses: Pierres fines et ornementales. Lausanne: Delachaux et Niestlé. p.108 

Zir-2. In Cours de base en gemmologie Gem-A. London, 2010

What Is Zircon Gemstone | Zircon Stone – GIA. (n.d.). Retrieved August 07, 2016, from http://www.gia.edu/zircon