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July-August 2013

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Collector's Note: Unusual Morganites from Corrego do Urucum, Galiléia, Minas Gerais, Brazil

BERYL CRYSTALS typically exhibit tabular or columnar habit with obvious hexagonal symmetry. Recently, specimens of lightly tinted morganite (lavender beryl) with a very atypical pseudo-isometric morphology from Corrego do Urucum, Galiléia, Minas Gerais, Brazil, have appeared on the market.

Figure 1. Pseudo-isometric morganite, 1.9 cm across, from Corrego do Urucum, Galiléia, Minas Gerais, Brazil. Jim Houran specimen, Joe Budd photo.

Figure 1. Pseudo-isometric morganite, 1.9 cm across, from Corrego do Urucum, Galiléia, Minas Gerais, Brazil. Jim Houran specimen, Joe Budd photo.

Figure 2. Idealized crystal drawing showing the dominant forms on the specimen in figure 1. Faces identified by contact goniometric measurements of interfacial angles.

Figure 2. Idealized crystal drawing showing the dominant forms on the specimen in figure 1. Faces identified by contact goniometric measurements of interfacial angles.

Frank and Wendy Melanson, of L'Amable, Ontario, Canada, returned from a 2011 buying trip with three morganites with an unusually complex combination of forms. The largest of the trio (3.4 × 2.6 cm) strongly resembled a John S. White specimen (fig. 3) from Urucum that Tom Moore identified as a “rare dihexagonal-bipyramidal [dihexagonal-dipyramidal] habit” (Moore 2009, p. 218). Collector Rich Olsen also has a similar example on matrix. However, the smallest two of the three crystals obtained by the Melansons showed a striking modification of this habit. The crystals exhibit roughly equal development of the dihexagonal-dipyramidal {312} faces and the basal pinacoid {001} along with lesser but significant development of the {101} and {102} hexagonal dipyramids. The effect is a “rounded” pseudo-isometric appearance reminiscent of garnet, analcime, and pollucite crystals.

Figure 3. Lavender morganite crystal, 3 cm, in a rare dihexagonal-dipyramidal habit, from Corrego do Urucum, Galiléia, Minas Gerais, Brazil. John White specimen, Jeff Scovil photo.

Figure 3. Lavender morganite crystal, 3 cm, in a rare dihexagonal-dipyramidal habit, from Corrego do Urucum, Galiléia, Minas Gerais, Brazil. John White specimen, Jeff Scovil photo.

Immediately recognizing their oddly stout form, gemologist Marc Fleischer purchased these two specimens. He kept the larger of the two (2.3 × 1.8 × 1.8 cm), and one of us (J.H.) acquired the other specimen (measuring 1.9 cm). These two are the only specimens we have seen with such a pronounced “rounded” appearance, and the smallest example pictured here (figs. 1 and 2, a near-“floater” crystal) shows it most distinctly. Still, White's and Olsen's crystals and the samples from the Melansons share common features: they are small, pale-colored, very gemmy, and lustrous. Not surprisingly, their depth of color appears to correlate with their crystal size and turbidity (the present sample appears very faint pink in fluorescent radiation and sunlight, whereas the pink tint is stronger under a fiber-optic halogen lamp). The crystal pictured as figure 1 has been tested in longwave and shortwave ultraviolet radiation and fluoresces white in shortwave with a “medium” intensity using a UV Systems, Inc., SuperBright shortwave (254-nanometer) ultraviolet lamp. A recent review of morganite from worldwide localities was given by Cook (2011).

ACKNOWLEDGMENTS

We thank Robert Cook and John White for reviewing the manuscript and Joe Budd and Jeff Scovil for providing the photographs.

REFERENCES

1. Cook, R. B. (2011) Connoisseur's choice: Beryl, variety morganite, San Diego County, California. Rocks & Minerals 85:1, pp. 50-57.

2. Moore, T. P. (2009) Collector profile: John S. White, Jr., and his single crystal collection. Mineralogical Record 40:3, pp. 215-23.

Jim Houran, a longtime mineral collector specializing in thumbnail-sized specimens, is a member of the Mineralogical Association of Dallas (MAD) and the host on the DVD series Mineral Perspectives (BlueCap Productions).

Dr. John Rakovan, an executive editor of Rocks & Minerals, is a professor of mineralogy and geochemistry at Miami University in Oxford, Ohio.

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