Comment from Sheila Sylvester - Brussels

“Tables of Gemstone Identification” written by Roger Dedeyne and Ivo Quintens

First edition 2007, published by Glirico – Gent (Belgium)  Cost €89 

The book is intended as a comprehensive yet relatively easy to use compilation of data to establish gemstone identity and to achieve this goal the book is divided into various chapters entitled Tables, as follows: 

Table 1:  Gemstones listed by refractive index (lowest RI value printed in red, and commercially valuable and synthesized stones’ names in blue and yellow respectively)

Table 2:  Opaque and translucent stones

Table 3:  Gemstones listed by density 

Table 4:  Spectra – as seen by a handheld diffraction grating spectroscope

Table 5:  Alphabetical index of about 600 entries with supplementary information

Table 6:  Glass – its wide-ranging values of refractive index and density shown as a graph

Table 7:  Garnet Group

Table 8:  Diamond Imitations – with a refractive index over 1.81 

As someone fascinated by the subject of gemmology and having had the opportunity to use several Tables of Gemstone Identification, I have found the Dedeyne/Quintens Tables extremely useful as the book contains all the information necessary to make a successful gemstone identification.   

After first establishing the refractive index and density values of any stone, one can immediately begin the identification process by referring to either Table 1 or Table 3 and cross-matching the various data relating to the particular gemstone under study.  For further confirmation of the gemstone identity, supplementary information is obtained in Table 5. 

After these checks, if not conclusive thus far, and if appropriate – referring to Table 4 to cross reference a spectrum (if possible as only 30% of gemstones show a spectra) can be diagnostic and all the gemstone spectra are conveniently assembled with detailed information on their respective absorption band patterns. 

The large groupings of gemstones are covered in Table 6 – Glass, Table 7 – Garnet Group and Table 8 – Diamond Imitations.  Within these tables – for example the Garnet Group – and to differentiate between solid solution series – colour and the spectra are of most use after the density and RI values.   Again, the relevant information is conveniently assembled within the Table and the chances of missing vital clues and information is much reduced.   

Similarly in Table 8 – Diamond Imitations.  After establishing whether these stones are isotropic or anisotropic, these stones can be some of the more difficult to identify.  The RI is generally over the limit for registering on a standard refractormeter and other methods may be within an error range and not definitive.  However with the neatly compiled additional information such as spectra (possible perhaps in only certain colours),  inclusions and remarks such as to check the UV, the assessment is made easier and more conclusive. 

The reasons why I find the Dedeyne/Quintens Tables so useful as compared to other books of Tables is because they are group-specific.  After reading the RI and/or density values of a gemstone usually gives one a fairly reasonable idea of its grouping.  Within the Dedeyne/Quintens  Tables it is possible to immediately consult all relevant information for a particular group of gemstone within a specific “table” or chapter.  Most other books of Tables tend to list all information in only one main table or section.  The chances of overlooking relevant data is greater using such Tables. 

The only possible disadvantage is the necessary bulk and size of the book containing the Dedeyne/Quintens Tables.  But this is a minor inconvenience for the advantages it provides in the comprehensive data contained within the “tables” or chapters within its covers. 

Sheila Sylvester
Gemmologist
Brussels