STUMPED! on a Rock from Baltimore's Stony Run

Many of us  collectors have rocks lying around  that we are unable to identify even when we know their locality. Ultimately, if determined enough, we figure it out. Often we find someone who can tell us, or we encounter a similar rock that's been identified. To date, no such answer has surfaced regarding the most definitive aspect of the rock pictured above.  Baltimore artist Rick Shelley---I was collecting with him at the time---pulled it  from the stream bed of Stony Run a short distance south of the Remington Avenue Bridge.

This is a section of the stream where mica schist, quartzite and quartz account for most of what is around. The latter two often bear stains of iron oxide. A few cobbles, when cracked open, show vugs bearing weathered hematite and/or goethite.  Less frequently, one might find a rock similar to this one where the quartzite bears a coating of drusy quartz that's become variably smoothed since entering the stream, The drusy quartz may or may not be botryoidal, as it is with this specimen

What everyone who  has seen this rock finds to be curious are the concentric circles. A likely conclusion could be that they are fossils, or fossil imprints. Although it's possible, even with with a matrix of quartz or quartzite, such an occurrence would seem highly unlikely at this location in the eastern section of Maryland's Piedmont.

Much if not most of the approximately one square mile of land surrounding where Mr. Shelley found this rock was once the site of various  filled in and built over gneiss quarries that yielded a diversity of interesting mineral species. These quarries and their minerals were the subject of numerous classical mineralogical reports. We are not aware of any literature noting the existence of  fossils in the area.
 
Very recently, we showed this rock to my friend John S. White, who having been Curato-in Charge of the Smithsonian's Division of Mineralogy for nearly eight years, could be the source of a credible opinion. After checking it out under the scope, he was as mystified as everyone else who has seen the specimen regarding its circles. His one firm opinion was to rule out the likelihood of a fossil.  His reasoning was as follows:

• I didn't see any organic looking surfaces.
• While there are a couple of prominent concentric circles, there are plenty of circles  that are quite irregular.
• There does  not appear to be any evidence of a sedimentary environment. 

What, then, expllains these circles?  We're hoping that someone will submit an answer about which he/she feels confident. 

The Mineralogical Legacy of Baltimorean Robert Gilmor

The important collection described below is the subject of a document excerpt  recently transmitted to me by John S. White, past Curator-in Charge of   the Smithsonian's Division of Mineralogy. He received it from Dr. Johan Kjellman, curator of the mineral collection at Uppsala University, Sweden. Dr. Kjellman had been researching crystal models and was interested in those that Albert Hauy had originally intended  for presentation to the Emperor of Austria. The excerpt below is  from The American Journal of Science and Arts, Second Series, Volume 6, November, 1848. In the note to which it was attached, Mr. White stated:  "Turns out that the old gentleman was Robert Gilmor (1774-1848) who, interestingly enough, was a Baltimorean. "

It did not take long for me to determine that in 1814, Mr. Gilmor published "A descriptive catalog of minerals occurring in the vicinity of Baltimore"  in  Bruce's American Mineralogical Journal, Vol.1, 1813, pp. 221-223. Therein he enumerated 43 different minerals found within a 14 mile radius of the city. Although Google had digitized this publication, the pertinent pages were missing from those that appeared on line. 

A Friday afternoon visit to Johns Hopkins University's Milton Eisenhower Library revealed that the publication we were seeking was available there on microfilm. The librarians were kind enough to locate it for me over the weekend, and by Monday copies were in my email. 

Here are some  items that proved to be of particular interest:

• "Native Magnesia:" From Bare Hills, obviously this is magnesite. "Is it not a carbonate of lime combined with magnesia?" Mr. Gilmor pondered. Even today, massive magnesite is quite common throughout the Bare Hills serpentine barrens. However, for it to be in crystals "accuminating to a dihedral summit---insulated, pure white and (or) transparent,"  is unheard of. 
• Corundum:  "An hexahedral crystal an inch in diameter was also found at Bare Hills, which in all its external characters corresponds with corundum, as described by Hauy; but the writer considers it doubtful"  Since then, corundum has been reported where pegmatite injects serpentine in other parts of Maryland. As a pegmatite dike adjoins the serpentine at the northern extreme of Bare Hills, the possibility of a corundum find seems realistic.
• "Staruotide is found in hexiahedral prisms with dihedral summits on the Falls Turnpike, 7 1/2 miles from Baltimore." This could be the same material  as collected by Bob Simonoff and very kindly confirmed for us as staurolite by Professor Emeritus Peter Leavans at the University of Delaware. It was the subject of our July, 2011 post 
• "Disthene:"--"or Cyanite, (lamellar) of a pale green (rarely blue) is found in a micaceous rock about 20 miles from town on the Falls turnpike, at Scotts Mill, 7 miles from the York Turnpike. The crystals are large and small, many of them 4 and 5 inches in length."
• Galena: "Found in a small vein in quarries about the first Falls Turnpike gate on the west side of Jones' Falls, accompanied by black lead ore and blende of sulphuret of zinc.  It is also asserted to be lately found in a large vein within 7 miles of the city, but the direction is kept a secret. The specimen seen by the wriiter, and said to come from the spot, was a large mass of galena." 

We have posted the document on our Maryland Minerals web site .  

Meanwhile, we have just received word from John White that Wendell Wilson, Publisher and Editor in Chief of Mineralogical Record, (which Mr. White founded in 1970) is interested in putting together an article about Mr. Gilmor, especially if he can come up with at least a couple of photographs of minerals bearing his label. Mr. Wilson's research suggests a possibility that perhaps one or two significant specimens once owned by Mr. Gilmor that were not included in the collection being sold in 1848 could have remained in Maryland. We are currently investigating that possibility. While the likelihood of locating these specimens is remote, our efforts could open new windows on mineral specimens collected in and/or housed in Maryland. 

John White and a Rock Pile

Actually we  were trespassing as we peered through a pile of rocks dumped just a few feet off a lonely country road in York County, Pennsylvania near Delta. John White and I  had  tried unsuccessfully to locate the landowner. In the process, we learned that the a local power company had dumped the rocks there in conjunction with a project that never happened. Hopefully, the landowner wouldn't mind.

John had expressed interest in these rocks over the past year and had encouraged me to check them out. He had described the material as "just serpentine rock."  For reasons that hindsight now renders lame,  I had not yet done so. What was wrong with me? When a past Curator-in-Charge of the national mineral collection who also founded Mineralogical Record gets excited about a site less than an hour's drive away, it's worth a look.

Then last week, John emailed me an invite to see some of the rocks he'd purchased at the recent Denver show. Attached was the image shown at left. It pictures cabs from material John had found when he first discovered the aforementioned rock pile last year.  His email suggested that after looking at his Denver acquisitions, we drive there.

We did and ended up crawling over the pile of serpentinite rocks. There were numerous pieces worthy of John's cabs. Antigorite was abundant, especially  the columnar picrolite variety. Colors ranged from  very light green to very dark green. Gemmy coatings of medium to dark green  antigorite occasionally comprised the rocks' surfaces. This antigorite was slightly translucent, but less so than antigorite (var.) williamsite.  It also lacked those chromite spots so definitive of williamsite. The  rock beneath the antigorite was grainy, dull greenish gray and black, possibly chrome-bearing, and iron-bearing almost for sure. Though we didn't have magnets, John had learned  when the cabs from his earlier find were made  that much of the black material here was magnetic.

One specimen that particularly interested me is the quartz (var.) prase shown at right. Is presence along with the serpentinite strongly suggests that the rocks on this pile were from the neighboring Cedar Hill or Penn-Maryland Quarries just a few miles east in Lancaster Couty at Fulton Township. Both quarries exploit the same kind of serpentinite rock that's part of the Baltimore Mafic Complex.

 Another piece that impressed me features an intersection of massive magnetite with pale green antigorite (var.) picrolite. Were it chromite rather than magnetite meeting that picrolite, I suspect some williamsite would be gracing the picture as well. Assuming that the rocks originated at either the Cedar Hill or Penn- Maryland Quarries, such a find would seem reasonable. Chromite as well as magnetite is known to occur at both localities

All told, we spent less than an hour at the rock pile. We departed because we were hungry and still marginally clean enough to be served a hearty lunch at a family restaurant a few miles away.

 Thereafter, we continued about ten miles further on  to check out ---with permission---the edges of another rock pile that John knew about. It consisted mostly of  "Wissahickon schist."  We quickly uncovered some graphite, pyrite, and siderite.  This was a much bigger pile of rocks. Unfortunately,  later commitments limited the amount of time we had to see as much of it as we would have liked. Stay tuned.

John S. White Compares Munich to Tucson

A May-June, 2009 article about John S. White by publisher Thomas P. Moore of Mineralogical Record (which John founded in 1970), mentioned how "some less than reverent visitors used to ask permission to dig in the hypothetical pile of discarded matrixes in John's back yard." Though more reverent than that, I had little compunction about eyeing the pebbles in his driveway as we walked out from his home in Stewartstown, PA for lunch at a restaurant in nearby Shrewsbury. The calcite and epidote in our title picture were the bounty.

John had recently returned from the annual late autumn Mineralientage München (Munich) show. Though my visit was primarily social, I was interested in learning as much as possible from John about how this event differed from the extravaganza that transpires from the end of January through the second week of February each year in Tucson.

Most significant, John noted, is that Munich has no fringe shows and no hotel selling. The event is open to the public for two days only and takes place at a single location, namely the four huge halls of Neuen Messe München. Each of these four halls is larger than the Tucson Convention Center.

Partial compensation for the lack of fringe shows and hotel selling is a policy at Munich that allows admission to certain high-end dealers and well-connected advanced collectors during set-up period, which begins on Wednesday and continues through the following day. Doors open for collectors on Friday. The general public gains admission only on Saturday and Sunday.

Mineralientage München consists of four "worlds:" Mineralworld, Gemworld, Fossilworld, and Stoneworld. While the titles tell the story, it's notable that Gemworld has a few gem minerals and that the wares in Stoneworld not only run a new-age gamut, but can include everything from interior acoutrements to hot stone massages.

My conversation with John focused mostly on Mineralworld. Along with world class exhibits---2011's Show featured European Classics---Mineralworld is divided into sections, halls unto themselves. The "super-premium dealers," as John descried them, operate from the most elaborate stalls in a walled in section. With dealers of all stripes in between, Mineralworld also accommodates dealers small enough to be clustered where each could have as little as a meter of space.

Scattered throughout are Chinese, Afghan, Pakistani, and Indian dealers. The quality and prices of their merchandise can vary from one hall to another. The Chinese dealers, says John, are likely to have the best material and the most new finds. Regardless of nationality, John emphasizes that as in Tucson, quality and prices are all over the map and often far from commensurate.

Moroccan dealers by the dozens are clustered in another hall and as at Tucson generally have more predictable inventory that varies little from year to year. The question was(is) how can they all make enough money to keep returning? The answer, John says is that they are there for many reasons, not just to profit on their mineral sales.

Notably different from the “Big Show” in Tucson, John states with emphasis, is that "excellent food courts are all over the place," with much better fare than available at the Tucson Convention Center. The catalog for the Munich Show is also a lot slicker than at Tucson. John gives me one shortly before I leave.

Walking once again the few steps across the driveway from his door to my car, I stoop to pilfer another pebble, because unlike the others, it's quartz. About to toss it later as the waning natural light in my office rendered little of interest to be visible, I opted first for a quick glance under the scope. Revealed was the phlogopite micromineral at left.