CHRONICLES OF CENTRAL PENNSYLVANIA MINERALOGY Part Six
Jay L. Lininger, Dillsburg, PA
In this, the sixth installment of the CHRONICLES series, I thought it might be of interest to discuss the history of two rare minerals found in the metavolcanic rocks of Central Pennsylvania. I'm referring to the species piemontite and scheelite. To the species collector, the opportunity to collect rarities in the field is always a special thrill, because they are usually elusive. The two species mentioned here fit into the elusive category in regard to their Central Pennsylvania occurrences. The first report of their occurrence here was made more than a hundred years ago. For those mineral collectors who take special delight in field collecting Pennsylvania minerals, the quest for piemontite and scheelite has been a century long span of occasional delight and abundant frustration.
PIEMONTITE: RUSTY EPIDOTE
Like the comedian Rodney Dangerfield "who didn't get no respect," piemontite has suffered a similar fate in its past history. This carmine-red colored member of the epidote family was referred to by many geologists as the "rust-colored epidote." This would imply its early recognition as a subspecies of the better known silicate mineral epidote, which is invariably recognized by its pistachio green color. Epidote is also a common constituent of the Central Pennsylvania metavolcanic rocks, though sparse in association with the rare piemontite. The species piemontite has now been recognized as a distinct member of the epidote group, a family of ten species which includes other familiar species from Pennsylvania. Among them are allanite, zoisite, clinozoisite, and, of course, epidote.
Piemontite, chemically a calcium, aluminum, iron, manganese silicate was first described from a location in Piemonte, Italy, from which it draws its name. Suffering from continuing "non-respect" its name was mutated to piedmontite in earlier American Mineral texts, and can be seen in that form in familiar publications, such as Sam Gordon's "Mineralogy of Pennsylvania." Although we have no record of who first found the mineral in the South Mountain metarhyolites Of Adams and Franklin Counties, it was first identified and described in the American Journal of Science in 1892 by Prof. George Huntington Williams of Johns-Hopkins University. Williams was a mineralogist and petrologist of some fame during the turn of the century. He had a special fascination with the altered rocks of the Blue Ridge Mountains (known in Maryland as the Catoctin Mountain and in Pennsylvania as the South Mountain). He encouraged one of his post-graduate students, Florence Bascom, to choose the study of the metavolcanics for her doctoral thesis. Bascom followed his advice, and in what was to become a landmark effort, she postulated the volcanic origin of the South Mountain basal rocks. In the process, she became the first woman to earn a PhD in the United States.
Williams joined Bascom in the field reconnaissance of the South Mountain rocks. He worked in the region north of the Lincoln Highway -- she worked south of the highway. During the summer season of 1892-1893, the two geologists collected thousands of rock samples from numerous out crops all along the range. Many of the specimens were an attractive brecciated pink metarhyolite of cuttable quality. Three of the locations produced rhyolite with beautiful radial crystallizations of a rich purplish-red mineral which Williams correctly identified as piemontite. Florence Bascom chose the Clermont House, a well known road house near the Maryland Line in Blue Ridge Summit, as her field headquarters. Blue Ridge Summit was a village of summer homes for the elite of Washington, and as such were well manicured. On the grounds of one such home near the Clermont House, Bascom encountered her first specimens of the lovely mineral. Weeks later she encountered a piemontite rich outcrop on a visit to the south flank of nearby Pine Mountain.
Williams also encountered an occurrence of richly crystallized piemontite in the Buchanan Valley, about two miles north of the Lincoln Highway. The Buchanan Valley was a rich fruit growing area, so it was natural that farmers would pick rock off the orchards and place it in stone piles. One such pile, a few hundred yards behind the dwelling known as Musser's Store, produced rich specimens of piemontite which contained a white mineral which was unknown to Williams. Later that year (1892), Williams found time to chemically analyze the mineral in his laboratory at Johns Hopkins. To his utter surprise, he identified the calcium-tungsten mineral scheelite. This unexpected discovery was a first for Pennsylvania, and although known to occur in contact metamorphic deposits, seemed totally out of place in this unique environment. Williams and Bascom both recorded their findings in great detail. Bascom also proved that some of the pink colored rhyolites drew their color from included piemontite. In spite of all their efforts, the piemontite scheelite occurrences were largely overlooked for the next several decades. The valuable study specimens of the especially rare scheelite were also lost during this period, perhaps due to theft or carelessness at Johns Hopkins.
The, 1920's and 30's saw the emergence of a young geologist who was to become a legendary figure in Appalachian geology. George W. Stose, a "hands on" geologist molded in the style of 19th century field scientists, would earn his reputation at the U.S. Geological Survey by his legendary field mapping abilities. Stose gained a special interest in the South Mountain metavolcanics, probably as a result of his association with Florence Bascom who was employed by the survey during the summers. Bascom gained esteemed scientific recognition for her founding of the geology department at Bryn Mawr, but also did geological mapping in the summer season. Perhaps it was no coincidence that Stose eventually married Anna Jonas, a top protégé of Bascom at Bryn Mawr.
About 1930, George Stose began a geological field survey of Adams County in a cooperative venture with the Pennsylvania Geological Survey. The result of this effort was the publication entitled "The Geology and Mineral Resources of Adams County, Pennsylvania" in 1932. Stose was able to report two more occurrences of piemontite which he found near the village of Wenksville during some earlier mapping assignments. The two locations, about a mile apart, produced the richest and most abundant occurrences thus far. This now brought the piemontite location count to five sites, and no further scheelite than the few original Williams specimens. In spite of the number of locations, the piemontite remained a rare commodity in Pennsylvania mineral collections, because the locality descriptions provided by the early researchers remained vague.
A NEW GENERATION
Once again, the minerals seemed to fall into obscurity during the ensuing years, and were almost forgotten. One solitary collector by the name of Robert G. Martin was the singular exception. Martin, a school teacher in the Waynesboro-School District, found much joy in exploring the copper mines and other mineral locations in Adams and Franklin County. During the 1920's and 30's Martin recovered many piemontite specimens from the Pine Mountain occurrence first described by Bascom. Martin traded and sold specimens during this period. I'm convinced that the occasional specimen which turns up with a Schortmann or Ward label, were likely to have been preserved through the efforts of R.G. Martin. Several years ago I acquired a piemontite specimen dated 1929 on a Lazard Cahn label. Its location was described as "Gladhill Station, South Mountain." The old Gladhill Station was on the south flank of Pine Mountain, and would have been a good way to better quantify the location. I believe this specimen could possibly have been a Martin specimen.
In the 1970's, the new crop of Pennsylvania collectors mentioned in previous CHRONICLE stories, began their assault on some of the old Pennsylvania locations. I had a particular goal to relocate the five original piemontite locations. It took several years to accomplish this goal, but I was able to relocate each spot. The Pine Mountain occurrence had been heavily altered by the GAF Quarrying operation, but some remnants of the original outcrop were still in place and specimens collected. A great thrill was the discovery from an early tax map, that the building known as Musser's Store was still standing -- now a private residence. With this firm landmark now established, an intense effort was made to relocate the original scheelite occurrence. False hopes were raised when a pure white mineral was found in association with piemontite near Musser's Store. This was identified by the late Davis Lapham as hyalite. A nice find, but not what we were looking for. We began to question the validity of scheelite.
Dr. Arthur Montgomery also questioned the validity of Williams original find. He suggested in his "Mineralogy of Pennsylvania 1922-1965" that Williams data for the specific gravity (5.61) was too low for scheelite. That is, unless some of the tungsten was replaced with molybdenum. Montgomery recognized that possibility, but was quick to note that no molybdenum had ever been found west of the Reading Prong, which was a hundred miles to the east. The suggestion seemed to be that Williams had made a mistake; and there were no verifiable specimens to prove otherwise.
Mother nature doesn't always go along with our preconceived ideas however, and unbeknown to our little band of intrepid field collectors, the scheelite picture was about to change. During the 1960's another geologist came onto the South Mountain scene. John Fauth, much like Florence Bascom and George Stose, became attracted to the South Mountain metavolcanics. Fauth had taken on some mapping assignments with the Pennsylvania Geological Survey, but during the course of this activity, was offered a full time teaching position at State University of New York (SUNY) in Cortland. His mapping assignment in the South Mountain became an 1 year summertime odyssey. In the process, he mapped every foot of metavolcanic rock and collected many thousands of specimens. Among them was a suite of piemontite rich rhyolite specimens which had been collected from an isolated outcrop near the old Bechtel copper mine north of Fountaindale, Adams County. Here was a new recorded occurrence for piemontite -- the first in more than 40 years. More importantly was the pure white mineralized segments in the vugs among the piemontite. An occurrence of scheelite had now been verified! Interestingly, the specific gravity was similar to the material reported by Williams. His unblemished record had now been verified. Also that of Art Montgomery who had hedged his bets by noting the possibility of molybdenum. The new material did indeed contain molybdenum. The new mineral appeared to be a transition species between powellite (the calcium molybdate) and scheelite (the calcium tungstate). The new "scheelite" remains a rare mineral, with only several dozen specimens recovered. But I have no doubt that other occurrences of both minerals yet remain, and some ambitious collector or serendipitous event such as construction digging will uncover more.
Of the six verified occurrences of piemontite, three still have specimen potential. The rhyolite piles in the Buchanan Valley about two miles north of the Lincoln Highway still yield good specimens for the diligent collector. Also, the two Stose locations near Wenksville still have specimen material. The owners of the orchards have been generous in allowing careful collecting on their properties. It is worthy of note that the classic "Gemstones of North America" by John Sinkankas, lists piemontite in rhyolite as semi-precious gem cutting material.
The two unusual minerals add to the lore of our Central Pennsylvania area. Piemontite has not been found outside of the South Mountain area, and scheelite has only one other rare occurrence in Pennsylvania -- a pegmatite zone in the old Hoffman Quarry in North Philadelphia. The only other Eastern location for piemontite was in a temporary construction site in Connecticut.