An Alexandrite-Emerald Intergrowth, Reportedly from Russia

Although many emerald deposits also produce alexandrite, particularly those formed in association with mica-rich schist, it is rare that both gems are found in such a close association that they can be fashioned into a single stone. This article details the examination of one such piece, reportedly originating from a deposit in Malysheva, Russia.

Alexandrite and emerald are the Cr/V-bearing varieties of chrysoberyl (BeAl₂O₄) and beryl (Be₃Al₂Si₆O₁₈), respectively, although Fe can also affect their coloration. The main chemical difference between the two minerals is that chrysoberyl lacks Si, which is a major constituent of beryl. In general, alexandrite and emerald are geologically rare because they require the simultaneous presence of both Be and Cr. While Be often occurs in geochemically ‘evolved’ rocks such as granitic pegmatites, Cr is commonly associated with mafic-ultramafic rocks. The intrusion of pegmatites into these rocks can result in the formation of mica-rich schist in the contact zone, and this is typically where alexandrite and/or emerald may crystallize. In some cases, alexandrite may occur together with emerald in these schist-hosted deposits (Giuliani et al., 2019; Sun et al., 2019). The close association of these gems has been described for various localities, including Malysheva, Russia (Schmetzer, 2010).

In September 2024, a 15.80 ct pear-shaped gemstone was submitted to Lotus Gemology’s Bangkok laboratory for identification. The specimen, reportedly from Malysheva, was purchased in rough form by the client, who later discovered during the cutting process that it consisted of an intergrowth of more than one mineral.

Figure 1. A vein of phlogopite occurs along a boundary between the alexandrite and emerald portions of the stone. Locally present within the phlogopite-rich area are zoned particle clouds. The tiny orange crystals adjacent to the phlogopite vein consist of the 2H-polytype of wurtzite. Photo: Kaylan Khourie; FOV: 3.3 mm.

The stone was first examined with a gemological microscope and then analyzed with confocal microRaman spectroscopy. These techniques showed that it consisted of about 75% translucent alexandrite, which was split into two sections: a large portion at the round end of the pear and a smaller area near the tip. Between the two was a zone of transparent emerald. A vein of phlogopite mica was present at one of the alexandrite/emerald boundaries, along with zoned particle clouds (Figure 1).

Figure 2. Phlogopite macrocrystals with apatite sub-inclusions in the alexandrite portion of the intergrowth. Photo: Kaylan Khourie; FOV: 5.1 mm.

Phlogopite was also present as coarse crystals in the larger alexandrite portion of the stone. Within these phlogopite inclusions were several smaller apatite crystals (Figure 2). Prismatic apatite was also found in abundance within the emerald portion and, interestingly, these apatite crystals contained phlogopite sub-inclusions (Figure 3).

Figure 3. Apatite crystals with phlogopite sub-inclusions in the emerald portion of the intergrowth along with chalcopyrite flakes. Photo: Kaylan Khourie; FOV: 5.6 mm.

Raman spectroscopy also identified tiny flakes of chalcopyrite (CuFeS₂) in the emerald section (Figure 3). In addition, the 2H-polytype of wurtzite ([Zn,Fe]S) occurred as submetallic orange crystals adjacent to the phlogopite vein (Figure 1). Sulfides are not uncommon in emerald: chalcopyrite and sphalerite (a polymorph of wurtzite) have been reported previously in emeralds from Malysheva (Popov et al., 2023) and unconfirmed inclusions of wurtzite/sphalerite were mentioned by Yu et al. (2000) in a Zambian emerald.

Unsurprisingly, the gem was fissure-filled (Figure 4), a common clarity enhancement applied to emeralds but also many other gemstones. The filler substance was reported by the client to be coconut oil.

Figure 4. After gentle warming with a hot point, oil leaked out of some of the fissures of this alexandrite-emerald intergrowth. The luster difference of the surface-reaching apatite crystals in the emerald portion is also apparent in this reflective lighting condition.
Photo: Kaylan Khourie; FOV: 5.6 mm.

The hydrostatic SG of the gem was measured as 3.38. This is consistent with the combined presence of alexandrite (3.71–3.76), emerald (2.65–2.78) and phlogopite (2.78–2.85). Observation of the stone with a long-wave UV torch (365 nm) revealed some interesting zonal features that gave clues as to the gem’s growth history, reflecting variations in Cr and/or Fe in the growth environment (Figure 5).

Figure 5. Microscopic observation while illuminating the stone with a long-wave UV torch (365 nm) exhibited zoned fluorescence that is likely related to variations of Cr and/or Fe in the different sectors of the gem and provides clues to the gem's growth history.
Left: Table-up orientation; FOV: 23.5 mm. Right: Table-down orientation; FOV: 23.5 mm. Photos: Kaylan Khourie.

The congruous formation of alexandrite and emerald requires sufficient supply of both Be and Cr, and the finite/localized presence of Si. It appears that the formation of this present specimen involved multiple crystallization episodes (cf. Ustinov & Chizhik, 1994). This is supported by the existence of different generations of phlogopite (i.e. as veins, large crystals and inclusions in apatite within the emerald portion), as well as two occurrences of apatite (prismatic crystals within emerald and inclusions within phlogopite crystals in the alexandrite).

While alexandrite-emerald intergrowths are seldom mentioned in the literature, examples do exist (Lyckberg & Zagorsky, 2000; Hainschwang, 2003; see also Alexandrite + Emerald). However, to the best of this author’s knowledge, a faceted example such as the one described here has not been documented previously.

REFERENCES

• Giuliani, G., Groat, L., Marshall, D., Fallick, A.E. and Branquet, Y. (2019) Emerald deposits: A review and enhanced classification. Minerals, Vol. 9, No. 2: 105, February, 63 pp.
• Hainschwang, T. (2003) An alexandrite-emerald intergrowth. Gems & Gemology, Vol. 39, No. 3, Fall, pp. 226–227.
• Lyckberg, P. and Zagorsky, V.Y. (2000) Gem pegmatites of the Ural Mountains, Russia. Mineralogical Record, Vol. 31, No. 2, pp. 177–183.
• Popov, M.P., Rassomakhin, M.A. and Demina, L.A. (2023) Rare mineralization from quartz-plagioclase veins of the Mariinsky deposit (Ural emerald mines). News of the Ural State Mining University, Vol. 71, No. 3, pp. 25–31.
• Schmetzer, K. (2010) Russian Alexandrites. Stuttgart: Schweizerbart Science Publishers, 141 pp.
• Sun, Z., Palke, A.C., Muyal, J., DeGhionno, D. and McClure, S.F. (2019) Geographic origin determination of alexandrite. Gems & Gemology, Vol. 55, No. 4, pp. 660–681.
• Ustinov, V.I. and Chizhik, O.Y. (1994) Sequential nature of the formation of emerald and alexandrite in micaite-type deposits. Geochemistry International, Vol. 31, No. 7, pp. 115–118.
• Yu, K.N., Tang, S.M. and Tay, T.S. (2000) Nuclear microscopic studies of inclusions in natural and synthetic emeralds. X-Ray Spectrometry, Vol. 29, pp. 178–186.

ABOUT THE AUTHOR

ACKNOWLEDGEMENTS

The author wishes to acknowledge the staff at Lotus Gemology for assistance in several aspects of preparing this article. Thank you to Karl Schmetzer for helpful discussions and reference assistance. A special thank you to my wife Taryn for all the support.

Notes

First published in the Journal of Gemmology (2025), Vol. 39, No. 5, pp. 410–411. This online version contains some additional material not found in the print version.