JADEITE - Canadian Institute of Gemmology

However, Hobbs (1982: 13) warns that "it is rare to see the full spread of refractive indices listed on
the property chart because" jadeite is a crystalline aggregate and "only one refractive index is easily
resolved with the spot technique." To obtain a birefringence reading, Hobbs (1982: 14)
recommends using the birefrengence blink technique that involves rotating a polaroid plate in front
of the refractometer. This technique is illustrated and described by Hobbs (1982: 13, fig. 13).
Jadeite has a specific gravity of 3.33-3.35. Field (2000: 3) reports that "most jadeite...will
remain suspended or very slowly sink in methylene iodide (di-iodomethane) that has a density of
about 3.32-3.33 at normal room temperature." Hobbs (1982: 15) also recommends using
methylene iodide when testing for jadeite and warns that "jadeite, and many jade-like materials, may
contain impurities that will cause the specific gravity to vary. Hobbs (1982: 15) also notes that while
three common jadeite simulants (grossularite, zoisite, and idocrase) have specific gravity values that
can be confused with jadeite's all of them have refractive indices that are a good deal lower than
jadeite's.
Spectroscopic analysis is a useful means of identifying jadeite. Moreover, as noted by Hobbs
(1982: 15), "the spectroscope is helpful in that both cut and rough, as well as mounted or loose,
materials can be tested." Read (1999: 281) discusses the appearance of jadeite when examined with
a spectroscope (also see Hobbs 1982: 15-17; Webster 1975: 228; Walker 1991: 39-40). He states
that there is a "diagnostic line in the blue; chrome-rich jadeite has a doublet in the red, and two
bands in the red-yellow. Stained jadeite has a band in the orange and one in the yellow-green (plus
the diagnostic line at 437 nm)." Field (2000: 3) adds additional detail:
green jadeite shows several bands in the violet, the strongest being at 437 nm. It is intense
enough to be discerned by reflected light and by transmitted light if the material is not too
opaque or too dark in colour to transmit well. Naturally green jadeite also shows three
chromium lines somewhat resembling steps or louvres in the red, at about 630, 660 and 690
nm; but above this is a light zone from about 670 to the end of the visible spectrum. In the
"natural green" spectrum just described, there is nothing but darkness above the 690 nm
band. Note however, that the band at 437 nm is present in both the natural and dyed
examples.
Huang (1999) provides data on the characteristics exhibited by jadeite when examined with a
Raman spectroscope:
The Raman modes of jadeite are 292 and 328 cm -1 (Na-O stretching mode); 374, 416, 434
and 576 cm -1 (Al-O vibrational modes); 524, 700, 779 cm -1 (Si-O bending modes) and 887,
986, 992 and 1040 cm -1 (Si-O stretching modes)... There is little variation in the wave
number of Raman modes with substitution of iron and chromium in jadeite. Slope of the
variation is negative with increasing substitution of iron and chromium.
Jadeite is studied along with fourteen other gem minerals and Huang provides a flow chart (page
311) showing identification procedures to separate one mineral from another. We shall return to the
question of identifying dyed jadeite below in the section of treatment of jadeite.
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