Wednesday, March 23, 2016

Greenbelt, Maryland’s Phosphate Concretions: 75 Years of Questions

We are grateful to John White and Marie Huizing for procuring  two photocopied articles from 1965 editions of  Rocks and Minerals. The first article is entitled “Unusual Mineral Locality at Greenbelt, Maryland” by French Morgan; the second is a follow-up article  by Dr. Ernest E. Fairbanks, entitled “Remarks on an unusual mineral locality at Greenbelt, Maryland .” The information in these articles proved essential for this post.

Maryland’s only significant phosphate mineral find resulted when in 1941, a knoll  was leveled in order to erect a WWV Broadcasting Station near Greenbelt, in Prince George’s County. Today, the Visitor Center for the NASA Goddard Space Flight Center stands directly on the site.  The above pictured image shows one of many unearthed phosphate-bearing concretion nodules that were collected there in the 1940’s.

It is notable that iron bearing sandstone concretions of similar external visual appearance are common in Prince George’s County northeast of Washington, DC.  However, the only phosphate mineral bearing concretions ever known to occur in the region are from this one specific locality.

Out of curiosity, the late Dr. E. E. Fairbanks of the U.S. Bureau of Mines procured a few of the concretions for examination. The verdict, presumably based on visual observation, was that the phosphate material was dufrenite.  Dr. Fairbanks then provided a number of concretions to Ward's Natural Science Establishment, which subsequently sold them to various dealers and collectors labeled as dufrenite . Some concretions also found their way to both the Smithsonian Museum of Natural History in Washington, as well as the American Museum of Natural History in New York.

During World War II, the U.S. Government closed the area around the towers to the public for safety reasons. However, by 1944, French Morgan and several other members of the Mineralogical Society of the District of Columbia obtained special permission to collect there.  The group collected several dozen concretions that apparently had rolled down a small hill from where grading for the radio towers had taken place. Some of these concretions proved to be more interesting than those found several years earlier.

 In his 1965 article in Rocks and Minerals Morgan mentioned finding limonite, goethite, opal (var.) hyalite, and beraunite  during these later 1944 visits as well as “red, yellow and white minerals as yet unidentified.”  He also   noted “shrinkage cracks lined with microscopic crystals of an unknown mineral.” Specimens of the crystals were submitted to the U.S. U. S. Geological Survey, where according to article they “created no excitement.”

Not until late 1949 or early 1950 did the U.S. Geological Survey become interested in the Greenbelt material. This was after and was probably prompted by a 1949 article in American Mineralogist  by the late Dr. Clifford Frondel entitled “The Dufrenite Problem.” Frondel's work  confirmed that after analysis, the material from the original 1941 find at Greenbelt  was in fact rockbridgeite rather than dufrenite. The article described rockbridgeite as “indistinguishable from dufrenite in its general appearance and confused with that species since earliest times.” Later in the article, Dr. Frondel went even further to refer to rockbridgeite as “identical in appearance with the fibrous varieties of dufrenite.”

Soon thereafter, the U. S. Geological Survey reported x-ray and chemical analyses of a new and unknown species from within Greenbelt concretion material. Subsequently, a new revision in Dana noted that a similar mineral had been found in Russia. A brief description concluded that additional verification was needed.  The new Russian find received the name avovskite.  More than a decade after this Russian discovery and in the midst of the Cold War, Morgan’s article in Rocks and Minerals article noted that “attempt (to obtain more information and/or a sample)  has been made through diplomatic, scientific, and other channels, but no trace of azovskite has been unearthed.”

 Morgan also claimed in his article that “at the very beginning,” he had been promised naming rights from an unnamed source should a  new species be uncovered. He suggested the new mineral be named named fairbanksite  (not to be confused with the lead tellurite fairbankite ) in honor of Dr. Fairbanks. The only reference to fairbanksite we have been able to locate is on Mindat, which describes it as “unidentified microscopic crystals in shrinkage cracks in concretions,” citing Hey’s Chemical Index of Minerals, 2nd Edition 1962.

Even today, the IMA describes the status of azovskite as “doubtful.” Fleischer's Glossary of Mineral Species (2014) does not mention azovskite; nor does either edition of Bernard and Hyrsl's Minerals and their Localities.   Mindat states that azovskite “appears to be a gel” and “may be identical to delvauxite.” Delvauxite, however, is amorphous and is not known to replace crystals of other species,  Still, it is interesting to note brown globular material appearing in shrinkage cracks of Greenbelt concretions that bear a visual resemblance to delvauxite. Delvauxite is not known to have been reported from Maryland.

Catalogued in the Smithsonian collection are numerous “azovskite” specimens, mostly from Greenbelt. The catalog states or implies that none of the specimens was ever x-rayed. A curious and lengthy PDF procured from the Internet describes azovskite as a mixture of  santabarbaraite and goethite.  Also observed on the Internet was an azovskite specimen from Hagendorf, Germany, offered for sale by a European dealer who described it as santabarbaraite and goethite on quartz.  For santabarbaraite to be replacing crystals of goethite hardly seems a stretch. In fact, one of the Greenbelt azovskite specimens catalogued in the Smithsonian collection names goethite as an associated mineral. Santabarbaraite, on the other hand, has never been reported from anywhere in the Americas, much less Maryland. Just as interesting is that the Smithsonian collection catalog gives the Crimean Peninsula as the locality for one of the azovskite specimens.  According to Mindat, the Crimean Peninsula boasts five santabarbaraite localities, far more than any other region or country on earth where santabarbaraite is known to occur.

After  Rocks and Minerals published Mr. Moore’s article in 1965, Dr. Fairbanks submitted his follow-up article entitled “Notes on the unusual mineral locality at Greenbelt Maryland,” In addition to gratefully concurring with Mr. Morgan’s nomenclature  suggestion, Dr. Fairbanks  raised an additional point that 37 years later would prove eerily prophetic. He stated:  

It is definitely odd that the small area in which the rockbridgeite concretions were found was the only one in that area where phosphorous was relatively abundant. A very prominent non-government geologist suggested that a huge dinosaur died here furnishing the phosphorous.  

In 2012,  published  that the well-known local amateur geologist and fossil hunter,  Ray Stanford, was instrumental in the discovery of two nodosaur tracks on the property of Goddard Space Flight Center. A heavily-armored plant eater, the species was known to reach the size of a small elephant. It received its name from the numerous spikes in its armor. Stanford uncovered the tracks during excavation for the new building pictured at left, photographed from the immediately adjacent Goddard Visitors Center. 

The most recent published research regarding the Greenbelt concretions appears in Lawrence R. Bernstein’s 1980 Maryland Geological Survey Publication Minerals of the Washington, D.C. Area, which evolved from an earlier 1975 U.S. Geological Survey Professional Paper (Volume 475, parts 1-4) by Mr. Bernstein. Therein Bernstein noted oral communication from  Mary E Mrose of the U.S. Geological Survey reporting  cacoxenite, lipscombite, phosphosiderite, and strengite in the concretions. Our research turns up no other evidence that lipscombite, phosphosiderite, or strengite were ever reported from Maryland. The same can be said for the beraunite that Morgan claims to have collected between 1944 and 1949.

Hopefully, there are facilities willing to provide further analyses. The possibility of a new mineral species being discovered  in Maryland would surely be significant. Maryland’s only other type locality mineral---for which no type specimen is known to exist---is carrollite, discovered  at the Patapsco Mine in Carroll County and named in 1852. Should analysis of any Greenbelt “azovskite” specimen reveal santabarbaraite, America’s first santamariaite find would similarly be serious mineralogical news.  And confirmed analyses of lipscombite, phosphosiderite, strengite, or beraunite would be a major contribution to what is known of Maryland’s mineralogy.