June 18, 2015 / Gemstone Iidentification using Raman Spectroscopy

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June 18, 2015 / Gemstone Iidentification using Raman Spectroscopy

Gemstone Identification using Raman Spectroscopy


An extensive variety of gem materials are available in the jewelry marketplace at present. However, in some cases such materials are sold with inaccurate information on their identity.

The examination of gemstones requires an effective, easy-to-use analytical method. Raman microscopic technique offers unique possibilities for non-destructive and non-contact gemstone analysis at submicron level. It is particularly topical in case of very small gems which are mounted in pieces of jewelry.

This application note describes the use of confocal Raman spectroscopy for the identification of authentic materials on the gem market.

Precious stones (diamond, emerald, ruby, sapphire, pearl, etc.) as well as semiprecious stones (alexandrite, chrysolite, turquoise, garnet, topaz, amber, coral, etc.) are very popular and extensively used in the jewelry industry.

The Raman spectra of individual gem materials are shown in Fig.1-9. Also, the Raman spectra of gemstones from the RRUFF spectral database are given in Fig.1-9 additionally. Each of the measured materials has the particular and clearly identifiable Raman spectrum.

Diamond is the most valuable gem. Zircon and cubic zirconia, the high-usage imitations of colorless diamonds, can be passed off as the more expensive diamonds. Such imitations are very much alike, but their Raman spectra are completely different (Fig.1-3).

Diamond (Fig.1) shows a strong Raman band at around 1332 cm-1 (C-C stretching mode), which is absent in the cubic zirconia (Fig.2) and zircon (Fig. 3). The spectrum of zircon shows multiple Raman peaks at around 350, 432 (Si-O bending modes), 969 and 1003 cm-1 (Si-O stretching modes). 

The next important  precious stone is ruby, a variety of the mineral corundum (Fig.4).

Prices of rubies are primarily determined by color. The most valuable stones are red. Pink, orange, and purple are the normal secondary hues in ruby. Imitation rubies are also marketed. Red spinels and colored glass have been falsely claimed to be rubies by unscrupulous gem dealers. Raman spectroscopy allows to distinguish genuine rubies and their imitations.

The Raman spectrum analysis can also help to easily identify tourmaline (Fig.5), nephrite (Fig.6), benitoite (Fig.7) and amber (Fig.8) from their substitutes.

Additionally, the Raman spectra can separate real from faux pearls. The real pearls have very characteristic Raman spectra (Fig.9).

 

Conclusion

Confocal Raman spectroscopy is an ideal method for the analysis of gemstones. Due to its non-destructive technique Raman spectroscopy is very useful for gem merchants, gemologists, gem collectors and others.

 

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.8. Raman spectra of amber

Fig.8. Raman spectra of amber. A Reference Raman spectrum (Howell G. M. Edwards, Analyst, 2004,129, 870-879) is shown on the right

 

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.9. Raman spectra of freshwater pearl

Fig.9. Raman spectra of freshwater pearl. A Reference Raman spectrum (Karampelas S., etc. Identification of treated-color freshwater cultured pearls, Bulletin of the Geological Society of Greece, 2007, pp. 794-804) is shown on the right.

 


SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.1. Raman spectra (λex= 532 nm) of diamond

Fig.1. Raman spectra (λex= 532 nm) of diamond

 

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.2. Raman spectra (λex= 532 nm) of cubic zirconia

Fig.2. Raman spectra (λex= 532 nm) of cubic zirconia

 

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.3. Raman spectra (λex= 532 nm) of zircon

Fig.3. Raman spectra (λex= 532 nm) of zircon

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.4. Raman spectra of ruby

Fig.4. Raman spectra of ruby

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.5. Raman spectra of tourmaline

Fig.5. Raman spectra of tourmaline

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.6. Raman spectra of nephrite

Fig.6. Raman spectra of nephrite

SOL instruments: спектрометр, рамановский микроскоп, эмиссионный спектрометр. Fig.7. Raman spectra of benitoite

Fig.7. Raman spectra of benitoite

 

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Capabilities Confotec™ NR500
                        
Application Confotec™ MR350, MR520, MR750