Tuesday, December 25, 2012

First Arizona occurrence reported for two rare earth minerals

Well-known Arizona geologist and mineralogist Ray Grant  discovered the occurrence of two rare earth minerals never previously found in Arizona.   [Right, allanite on smoky quartz, White Mountain Wilderness, Lincoln County, New Mexico .   Credit, Rob Lavinsky, iRocks.com, under a Creative Commons license].  Ray's  report is published in the Mineralogical Society of Arizona’s  The Rockhound Record (December 2012 - p15).

The report is reprinted with permission of MSA:
Arizona Mineral Collector Number 153 By Dr. Raymond Grant

The Kingman Feldspar mine is located a few miles north of I40 on the east side of Kingman. I was there quite a few years ago, and at that time it was very easy to drive to and could be seen from a distance. I bring it up this month, as it is location of a number of new minerals to add to the list of Arizona mineral species. There are two references, one in Rocks and Minerals, volume 82, page 236-237, May/June 2007, it is an abstract “Rare-Earth Mineralogy of the Mohave County Pegmatites, Northwestern Arizona”, and the other is in the Canadian Mineralogist, volume 50, page 815-824, August 2012 and is titled Allanite-(Nd) from the Kingman feldspar mine, Mohave pegmatite district, northwestern Arizona, USA.

The nomenclature for minerals such as allanite that can have different elements predominate is to add a suffix showing the major element. Each of these minerals is considered a distinct species. In the Mineralogy of Arizona we just listed the mineral as allanite, but based on the new research we have two minerals allanite-(Ce) with cerium and allanite-(Nd) with neodymium. Allanite-(Nd) is a relatively new mineral, and this is the first verified occurrence in the United States. When I was at the mine there was a lot of allanite exposed in the walls. I had a crystal (rough shape) over a foot long. It was quite radioactive, and I’m not sure where I stashed it. I think it is in the
yard someplace.

The above references list thorogummite (new for Arizona) as inclusions in the allanite. This is part of the source of the radioactivity. They also report aeschynite-(Y) and bastnasite-(Ce), both of which are new for the Arizona list, giving us four new minerals for Arizona. Monazite and xenotime were also found and these were determined to be monazite-(Ce) and xenotime-(Y). Previously they were just listed in the Mineralogy as monazite and xenotime.

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