Print full article

Shades of jade: Are you selling the real deal?

Jade simulants

This white 'cabbage' jade from China's Qing Dynasty is valued at $900,000 US.
This white ‘cabbage’ jade from China’s Qing Dynasty is valued at $900,000 US.

Slightly harder though not as tough, green jadeite jade is most commonly confused with nephrite jade. A relatively new material, it was introduced to China from Burma in 1784 and is often mislabelled as ‘Chinese jade,’ since prior to 1951 there was no clear border between China and Burma. At the time, it was presumed the jadeite had actually been found in the Yunnan province of China.

While many green translucent gems like serpentine or chrysoprase look like jadeite and nephrite to the naked eye, their gemmological properties are quite different and easily identifiable based on RI, under magnification (Table 1, page 6), and using visible and infrared spectroscopy.

Omphacite and jadeite have long been considered easily distinguishable from one another, although the former is typically a dark green to black material that has higher optical properties. While standard gemmological properties may indicate jadeite, omphacite’s texture is slightly more granular than normal. The Gemological Institute of America (GIA) and other major labs are using Raman spectroscopy to distinguish jadeite jade from omphacite, but Canadian labs have not yet encountered any such specimens.

Identifying jadeite jade using standard and advanced instruments

An infrared spectrometer is a key advanced instrument used to identify 'A' jade from 'B' jade.
An infrared spectrometer is a key advanced instrument used to identify ‘A’ jade from ‘B’ jade.

Standard instruments like refractometer, microscope, and spectroscope can be used to identify material as jadeite jade based on its refractive index of 1.66, characteristic granular interlocking structure, visible spectra of 437 nanometer (nm) (due to iron), and fine lines at 690 nm (due to chromium) in the case of the green variety. Advanced instruments (i.e. infrared and visible spectrometer) are necessary to determine whether the colour of jadeite jade is natural or treated.

Seen in Figure 6, a Fourier transform infrared spectroscopy (FTIR) is a powerful tool for identifying the types of chemical bonds found in gems by producing an infrared absorption spectrum that is like a molecular fingerprint. It is used in gem labs to distinguish natural colour from polymer-treated jade, as well as identifying the natural or synthetic origin of diamonds and other gemstones.

UV-visible-NIR spectrophotometer measures how a gem absorbs light in the 200- to 1100-nm range and is used in gem labs for the detection of:
• gem variety (i.e. to distinguish nephrite from jadeite jade); and
• colour origin (i.e. natural colour versus dyed jade).

Visible spectra of natural (blue) and dyed jadeite jade (red) showing broad band in the red part of the spectra.
Visible spectra of natural (blue) and dyed jadeite jade (red) showing broad band in the red part of the spectra.

Also known as ‘A’ jade, natural-coloured jadeite jade is the rarest and most valuable type of this material. Without impurities, jadeite is white, but it can also be lavender (due to the presence of manganese, titanium, gallium), green (due to chromium), red (due to hematite), and yellow (due to ilmenite). There is a great deal of treated jadeite jade on the market, and much of it may not be properly disclosed.

Polymer-treated jadeite jade (known as ‘B’ jade) is first bleached to remove unwanted brown, yellow, and black stains and then polymer-impregnated to improve transparency. Structural damage occurs with this treatment, making the jadeite brittle. A chalky blue reaction under long-wave UV light is a good indication that jadeite has been polymer-impregnated, but the definitive test is infrared spectroscopy, which shows polymer peaks around 2900 cm -1 (wavenumbers).

Dyed jadeite jade is known as ‘C’ jade. It has additional amounts of chromium when dyed green, so the absorption band at 670 nm will be wide and strong, while natural-coloured jadeite has fine absorption lines of about 690 nm (Figure 7). The colour is unstable and fades under high heat and over time. The dye can be added to the polymer during the impregnation process, and the result is a chemically bleached, dyed, and polymer-impregnated jade (‘B+C’ jade). Dyed cracks may be visible with the use of a microscope (Figure 8, page 4). In addition, dyed jade fluoresces medium to strong greenish yellow, while natural-coloured jade usually does not exhibit any fluorescence.

Leave a Comment

2 comments on “Shades of jade: Are you selling the real deal?”

  1. Excellent article. Discovered Canadian jade after wandering into a store in Vancouver. Very interesting to learn more. Thanks for posting.

Leave a Comment

Comments

Your email address will not be published. Required fields are marked *