Quick identification of Pezzottaite

Mikko Åström & Alberto Scarani

Experienced gemologist has no difficulties in separating pezzottaite from pink beryl. The color of pezzottaite looks deeper with stronger pleochroism and it’s RI is higher than what is expected from typical beryl. Actually, pezzottaite is more likely confused with pink tourmaline especially in case of rare and beautiful cat’s eye stones. Raman spectroscopy offers a fast and convenient method for identifying this unique material unambigously.

Figure 1 shows broad scan spectra of pezzottaite and pink variety of beryl aka. morganite. Both gems have distinct Raman peaks at area 3500-3600 cm-1 caused by water molecules trapped in to channels of their crystal lattice. The peak at 3550 cm-1 distinguishes pezzottaite, it does not occur in beryl. Additionally, pezzottaite tends to produce increasing general luminescence towards higher wave numbers.

Figure 1: Broad scan (GemmoRaman-532nm) spectra of pezzottaite and beryl (shifted vertically for clarity)

Figure 2 shows the same spectra as above but zoomed into Raman fingerprint area between 250 and 1600 cm-1. While looking very similar at first glance, pezzottaite exhibits an distinct band at 1100 cm-1, which has not been observed in the Raman spectra of beryl. Automatic spectral matching algorithms of GemmoRaman-532 are typically powerful enough for making this separation but it’s advisable to pay attention to this area whenever the result of beryl or pezzottaite are given.

Figure 2: Raman fingerprint zone (GemmoRaman-532) of pezzottaite and pink beryl (shifted vertically for clarity)

References

Brendan M. Laurs, William B. (Skip) Simmons, George R. Rossman, Elizabeth P. Quinn, Shane F. McClure, Adi Peretti, Thomas Armbruster, Frank C. Hawthorne, Alexander U. Falster, Detlef Günther, Mark A. Cooper, and Bernard Grobéty: PEZZOTTAITE FROM AMBATOVITA, MADAGASCAR: A NEW GEM MINERAL

Further reading

Brendan M. Laurs, William B. (Skip) Simmons, George R. Rossman, Elizabeth P. Quinn, Shane F. McClure, Adi Peretti, Thomas Armbruster, Frank C. Hawthorne, Alexander U. Falster, Detlef Günther, Mark A. Cooper, and Bernard Grobéty: PEZZOTTAITE FROM AMBATOVITA, MADAGASCAR: A NEW GEM MINERAL

Laurs et al., Gems & Gemology Data Depository, Spectra: IR Absorption, Raman, and X-ray Diffraction (1/20/04)