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September-October 2014

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Letters

TWISTED AND BENT

As the author of the Mineral Mysteries column titled “Curved, Bent, and Twisted Crystals” (Rocks & Minerals, November/December 2012, pages 550–553), I was delighted to observe two more excellent examples at the 2014 Tucson Show. Both are kyanites from Brazil. The larger one is 10.4 cm across and is a Vasconselos specimen from the Cruzeiro mine, Sao José da Safira, Minas Gerais. The smaller, upright one is 4.2 cm tall and is a Luiz Menezes specimen from Distrito de Barra do Salinas, Coronel Murta, Minas Gerais. Both are with quartz. Mark Mauthner took the excellent photographs.

The two twisted and bent specimens from Brazil.

 

POLYHEDROIDS

It was with great pleasure that I read John White's Mineral Mysteries column titled “Polyhedroids” in the May/June 2014 issue (pages 275–278). I was well aware of their existence but unaware that there was a term describing them beyond the layman's term of box quartz. Approximately twenty years ago while collecting at a now-inaccessible place called the Brasie Corners quartz locality, in St. Lawrence County, New York, I was able to excavate a specimen of one of these unusual mineralogical oddities. Having seen it in situ, I can comment directly on its origins and perhaps provide some insight on how it may have formed.

The specimen pictured here was found while I was removing large quartz crystals (up to a foot long) from a large fracture in an area approximately 3 feet across that was similar to a pocket only not self-contained. The pocket material had collapsed and was in a jumble, filling most of the large opening. The entire opening contained translucent, milky to colorless quartz, and open space was rare. The large chunks of crystals, smaller shards and fragments of quartz, complete crystals, and this polyhedroid were all lying against one another in their post-pocket-collapse positions. The polyhedroid was found between the faces of several large quartz crystals and came out with well-developed sides and no symmetry—similar to those White mentioned in his article. Although perhaps not evident in the photo, all the sides are very smooth and triangular in shape. Small voids along the contacts between planes give it the rough appearance seen in the photo.

Within this opening everything seemed to be grown together and healed, if you will, by secondary quartz deposits that had filled most of the voids between crystals. Many crystals were brecciated, as was the material between them. Calcite, if ever present, was absent. Most of the material in the space had not fully grown or adhered to the materials next to it. If it had, there would have been nothing to collect that day other than one 600–700-pound block of quartz.

Close inspection shows that this polyhedroid contains numerous shards and crystal fragments, each of which was individually added to by secondary quartz growth within the opening. These shards and crystal fragments did, however, adhere to one another, creating this polyhedroid. Only a few tiny open spaces between the brecciated materials remain, most along the contacts between its triangular surfaces. It seems clear that this polyhedroid, recovered so long ago, is another twist on these interesting mineralogical curiosities.

Polyhedroid, 9 cm, from the Brasie Corners quartz locality, St. Lawrence County, New York. Michael R. Walter specimen.

 

PHOTOGRAPHY SEMINAR AND PHOTO COMPETITION

The fourteenth annual seminar on mineral photography will be held at the sixty-first Tucson Gem and Mineral Show in the Copper Ballroom of the Convention Center on Thursday, 12 February 2015, 1–3 P.M.

Regarding the photo competition, winners will be chosen by a panel of judges and announced the following Saturday evening (14 February) at the awards banquet. A cash prize will be given for first place in each category. The rules are as follows:

  • 1. No more than two entries are allowed per person.

  • 2. Slides must be original 35-mm transparencies in standard 2-inch mounts.

  • 3. Written on each slide must be the mineral name, locality, and size, either “macro” or “micro” category, and the photographer's name and postal address.

  • 4. Entries should be mailed to me at the address below, to be received by 15 January 2015, or hand-delivered to me at the Tucson Show. (All entries will be returned.)

  • 5. In addition to slides, digital images as high-resolution JPGs are also acceptable and can be mailed to my email address. CDs can be mailed to my postal address.

 

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