Zircon is a natural stone that, in my opinion, has a name too close to a synthetic stone called: zirconium oxide, cubic zirconia (sometimes CZ), or zirconium.

This proximity casts a veil over the potential of this beautiful stone offered by Mother Nature.

It still has enough hardness to be set in fine jewelry, and its sub-adamantine luster makes it a gemstone of choice.

A jewelry stone? Yes, jewelers use it as a center stone. However, this gem deserves to be worn with care. It is advisable to remove the ring for daily tasks that could scratch it.

High and low zircon: meaning?

Zircon contains a tiny (not harmful to health) amount of uranium and thorium in its atomic structure.

The material will therefore degrade over time (rest assured, we are talking geological time scales and human lifespan), and more precisely, it can be said to become amorphous.

Low zircons appear greenish to brownish and are called 'metamict zircons'. Sri Lanka is one of the best-known sources for these stones, but they can also be found elsewhere, like in Myanmar.

The difference is mainly in color and gemological properties. Whether high or low, zircon can be very attractive in both cases.

Gemological characteristics of zircon

Crystal system: tetragonal

Optical nature: Uniaxial (high zircons) to nearly isotropic (low zircons)

Refractive index: High zircons 1.92–1.99, Low zircons 1.78–1.90

Birefringence: 0.059 in high zircons to nearly zero in low zircons

Density: 3.9 to 4.8

Hardness: high zircons 7.5, low zircons 6.5

Colors: red, brown, yellow, colorless, blue, green, violet, pink, etc. Very diverse

Luster: Sub-adamantine (high zircons) to vitreous/bright (low zircons).

Spectroscope: Uranium spectrum, the diagnostic absorption line is at 653 nm

Identification of high zircon?

High zircons are very easy to identify; they show strong birefringence resulting in doubled facet edges in a cut stone. Visible under a loupe and often to the naked eye.

We will also note the sub-adamantine luster of this gem.

Observation under a polariscope will show an anisotropic gem. If the interference figure is visible, the gem is uniaxial.

The refractometer will indicate that the gem is OTL: 'over the limit'.

The high density of the gem provides an additional clue for identification.

The spectroscope will reveal the uranium spectrum with a characteristic line at 653 nm.

Identification of low zircon?

These stones can be confusing during a gemological examination as they are optically very different from high zircons.

For identification, they may show abnormal extinction under a polariscope due to the amorphization of the gem structure.

Density will be lower than in high zircons, and the refractive index will still be OTL on the refractometer.

The refractometer will indicate that the gem is OTL (over the limit).

Two tests should be remembered to help identify these gems:

- The spectroscope will reveal in most cases the uranium spectrum with a characteristic line at 653 nm.

- Examination of inclusions under magnification will reveal the amorphization of the material. Some inclusions in the shape of circumflex accents are characteristic of this type of stones.

Zircon and the art of cutting?

I would say this stone is not fragile to cutting but rather sensitive to heat in terms of color. Prefer cold bonding to avoid surprises.

If you want to reduce the doubling effect, it is better to cut with the table oriented perpendicular to the optical axis.

It is a pleasant gem to work with, polishes well, good cutting.