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March-April 2016

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Letters

UNUSUAL MORGANITES

This is a short follow-up to the Collector's Note article titled “Unusual Morganites from Córrego do Urucum, Galiléia, Minas Gerais, Brazil” by Jim Houran and John Rakovan (July/August 2013, pages 378–379). The authors mention the beryl crystals Frank Melanson brought back from a buying trip in 2011, and I wanted to share photos of the larger one described in the article (the one similar to John White's specimen, shown in figure 3 of the same article). I had promised photos of my specimen to Jim for an article if he wrote one. When the time came, as life would have it, my photo equipment was packed for our move to Bancroft, and then soon my collection was packed away too. So, as long overdue as they are, here are two photographs of that crystal.

Two views of an unusual morganite crystal, 3.4 × 2.6 cm, from Córrego do Urucum, Galiléia, Minas Gerais, Brazil. Raymond McDougall specimen and photos.Two views of an unusual morganite crystal, 3.4 × 2.6 cm, from Córrego do Urucum, Galiléia, Minas Gerais, Brazil. Raymond McDougall specimen and photos.

Two views of an unusual morganite crystal, 3.4 × 2.6 cm, from Córrego do Urucum, Galiléia, Minas Gerais, Brazil. Raymond McDougall specimen and photos.

MINERAL MYSTERY REVISITED

In my Mineral Mysteries column titled “Quartz Cores in Tourmaline Crystals” (September/October 2015, pages 462–466), I noted that pink (rubellite) cores of many color-zoned elbaite (tourmaline) crystals are often dissolved away leaving a hollow shell of green tourmaline that is completely unaltered. Lacking in the article were photographs of really good examples of this dissolution “in progress” because I had none to photograph. However, at the 2015 Colorado Mineral and Fossil Show in Denver, a Brazilian mineral dealer (Vasconcelos) had a tray of fragments from what I assume was once a large crystal, or several good-sized crystals, and these fragments beautifully illustrate partial alteration of the pink cores of a zoned elbaite (see photo). In this example the alteration appears to have proceeded from the center of the crystal (or crystals) because the interior has been altered to lepidolite, a lithium-rich mica, while there remains a zone of unaltered rubellite next to the completely unaltered green outer zone. I was very pleased to find this fine example that adds strong support to the interpretation of events presented in my article.

Partial alteration of the pink core of a zoned elbaite. The specimen is 4 cm across and is from the Cruziero mine, São José da Safira, Minas Gerais, Brazil. John White photo.

Partial alteration of the pink core of a zoned elbaite. The specimen is 4 cm across and is from the Cruziero mine, São José da Safira, Minas Gerais, Brazil. John White photo.

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