An All But Forgotten Maryland Gypsum Find

by Jack Slagle, June 19, 2010. Submitted by Dan Teich, MSDC President, for inclusion in this newsletter.

Among the most spectacular mineral specimens known to have been collected in Maryland are the blades and rosettes of gypsum (referred to as selenite when crystallized) that have been plucked from clay along the banks of the St. Mary's River at Chancellors Point and at Fort Washington in Prince Georges County beneath the bluffs of the Potomac. Lesser known, arguably more spectacular, and all but forgotten, are crystals collected approximately 50 years ago from a deposit near Fort Foote in Prince Georges County about three miles down river from Fort Washington.

For the second recent Sunday afternoon in a row, I had the opportunity to accompany Jeff Nagy on a drive to Strasburg, Virginia for further research on his project to update and republish the 1981 Maryland Geological Survey publication Minerals of the Washington, DC Area by Lawrence Bernstein. Specifically, his mission was to meet and learn about the find from Gary Allard, who with his brother Brian, now deceased, had discovered the deposit.

For its year and a half of productivity, the site was the secret domain the two brothers. Gary appears in our title picture holding a rosette and the most spectacular crystal blade of the find, which is the largest crystal of selenite I've ever seen from Maryland. Amazingly, its appearance suggests that it could once have been part of a rosette. Gary was photographed holding this same crystal 49 years ago in an article titled Crystals by the Ditchful in the June-July 1961 edition of Rocks and Minerals.

Over less than two years, the two brothers pretty much cleaned out most of the crystals, using some for a science project at school and selling others to classmates. Then they notified Ellsworth Swift, who authored the article in Rocks and Minerals. By then, the ditch had become less a source of crystals than what Swift referred to as "a challenge to discover the nature of the deposit and a chance to speculate on its formation."

Swift noted in the article that the Fort Foote crystals occurred in the Patapsco Clay, which also hosted other gypsum finds reported from the region. He described this clay as having formed in the Cretaceous Age and variegated (in color). Gary Allard recalled that the crystals occurred in a "purplish" clay that was darker than the crystal bearing Patapsco clay near Fort Washington. The crystals that Gary and Brian collected, including both rosettes and single crystals, were generally larger and less stained by clay than most of the better known material collected at Fort Washington and in St. Mary's County.

Particularly interesting was that while the riverside bluffs had yielded the Fort Washington and St. Mary's crystals, those from Fort Foote were collected about a half mile inland in a ditch intended for drainage alongside what was soon to be paved over as an extension of River Bend Road. Just as noteworthy was their confinement to a 125-foot section of the ditch.

Swift suggested that this could mean the crystals "concentrated along structural features such as joints," or that this particular deposit was "irregular in shape with the ditch merely cutting a cross section through the crystal patch.'" He explained further how the crystals were most likely formed when groundwater from the Piedmont that contained sulfuric acid from decomposing pyrite flowed eastward and mixed with the lime bearing beds of the Coastal Plain at Fort Foote.

Gary Allard now lives in the Shenandoah Valley near Strasburg, Virginia. He said he moved there because it had more kinds of rocks than "that boring Coastal Plain" where he grew up." He still loves to collect minerals and prior to his recent retirement was a jeweler and metal engraver.

One of his recent finds that amazed Jeff and me was the green quartz crystal pictured above from a location near Front Royal in Warren County, Virginia. The book Minerals of Virginia, by R.V Dietrich, 1991, noted nothing like it from Warren County. The only green quartz the book mentioned was presumably massive and from another part of Virginia with coloration "probably due to included amphibole or chlorite." It too, Gary discovered along the side of a dirt road and not in a ditch.