Opal at Bare Hills

Most likely opal is not uncommon as a coating on the serpentinite rock at Bare Hills along either side of Falls Road about a mile north of the Baltimore City line. Yet, I doubt that opal is on the radar of those prone to collecting here. At least, I've never heard anyone mention it, nor had I ever seen any Bare Hills opal. My only awareness of opal at Bare Hills was that Ostrander and Price's long out of print Minerals of Maryland (1940, Natural History Society of Maryland) named it as one of the species occurring at the two adjacent and long abandoned Bare Hills Serpentine Quarries as well as the surrounding barrens once dotted with chrome pits.

For the sake of reference, the image at left shows the westernmost and better recognized of those two former serpentine quarries along Falls Road. It was a good collecting spot until fenced off and declared off-limits by its owner, the Gerstung Inter-sports facility located at the end of Coppermine Terrace*. More accessible on the other (east) side of Falls Road, its presence mostly obscured by vegetation, is the second abandoned Bare Hills Serpentine Quarry. The ultramafic rocks comprising its talus, while not as interesting as the rocks I remember from years ago at the western opening, yielded my opal (var.) hyalite.

A dull blue-grey glint on a rock encrusted with tiny whitish globular dots caught my eye. Observing through the loupe, I assumed the dots to be magnesite or hydromagnesite, which ubiquitously forms massive coatings on similar rocks throughout the Bare Hills area. The globular presence was distinct enough that it prompted me to bring the piece home for a look under the scope. The right side of this post's title image shows the surface of this rock at 40x. No question that the coating is opal, whose obscurely reported presence at Bare Hills had mystified and fascinated me for more than 50 years.

Since the appearance of this rock was so similar to hundreds of rocks hereabouts, I suspect that opal may not be that elusive at Bare Hills. This certainly was not the first time I'd seen rocks in the area that were visually similar, at least at first glance. Otherwise, except for occasional birdseye chromite in weathered serpentine rocks along with a few veins of chrysotile, there seemed less that was likely to interest collectors than I recall from years ago at the quarry on the other side of Falls Road and the chrome pit dotted serpentine barrens surrounding it.

Though off-limits where not built over, my hunch is that those barrens on the west side of Falls Road, unlike those on the east side of Falls Road that surround the site of my recent visit, always were and still could be more interesting. They will be the topic of a Mineral Bliss post at some point in the future.

*It could be that the name of "Coppermine Terrace" was conceived in ignorance. In its entirety, Coppermine Terrace passes exclusively through serpentine barrens formerly worked for chromium only. The site of the former Bare Hills Copper Mine is approximately two miles away and set in a completely different landscape.

Bob Conkwright Reflects on his Giant Maryland Corundum

Our recent Jan. 6 topic, "An Humongous Maryland Corundum," gleaned more hits than any previous Mineral Bliss post has ever received. How did this specimen get to where Bob Conkwright, Jr. found it back in 1960 amidst the dumps of one of the Devries Quarries, which even then were long defunct? Regardless of whether the piece was actually quarried there, which is open to question, we can be quite certain at least that it formed close by, somewhere near this Henryton Tunnel less than a mile north of Marriottsville.

When we spoke late last December in Bob's office at the Maryland Geological Survey, he referred to this find as "my heritage," and needless to say it had much to do with how and why he went on to make geology his career. Surely Bob has given plenty of consideration to where this amazing specimen came from and how. Here are his thoughts:

There are many references available on corundum digenesis. Looking at page 90, “Geochemical Methods of Prospecting for Non-metallic Minerals”, (Komov, I.L., 1994)*, the author indicates six recognized primary corundum deposits. Corundum is commonly associated with mafic and ultra-mafic rocks (silica-poor), pegmatites (which are typically not silica-poor), and marble (which can be relatively silica-poor). If you look through the various scenarios for corundum formation, a couple of items stand out. Bedrock in the Patapsco Valley has pegmatite and marble, and in places, pegmatites intruding marble. According to the 1928 Carroll County geologic map, the easternmost Henryton pegmatite dike is in contact with Cockeysville marble. The pegmatite/marble associations in the valley are known to include albite, diopside, phlogopite and pyrite, all minerals listed as associated with corundum. Given the size of the crystals, the corundum mass is almost certainly pegmatitic in origin, and the Cockeysville marble could have supplied the necessary silica-poor environment for the reaction to occur. Given the large size of albite and diopside crystals known to exist in these formations, I think it is not unlikely the pegmatites that injected into the marble are a likely source.

I have not found any mapped occurrences in this part of the State where pegmatites intrude silica-poor ultramafics or serpentinites. This has occurred around the Pennsylvania border, and corundum is known to occur in those formations. Red corundum crystals were reported in pegmatite-associated serpentine, which also produced talc, actinolite, chlorite and other silica-poor minerals **. There are soapstone quarries in the Patapsco area, so perhaps there are pegmatite-injected serpentinites that have not yet been identified.

Since the large crystal size would indicate a pegmatite source, but no known pegmatite dikes are injected into these local, silica-poor rocks, I suggest the specimen came from the local marble. This leaves the mystery of the reddish color, known to be derived from trace chromium. I have an idea, which might be a bit lame, but it is the only one I have for now. According to the 1993 Geologic Map of Howard County, John Edwards interprets the Patapsco Valley pegmatites as Silurian in age. The mafic and ultramafic complexes in the region are interpreted by Edwards as older than the pegmatitic injection. Could it be that the injected magma picked up some chromium ions during the intrusive event into the older marbles? Perhaps.

I am certain the corundum mass was loose in dump material, or possibly just in the soil/saprolite layer. Given the hardness of corundum and the rapidity with which calcite and feldspar weather, it is not unreasonable to assume the crystals, if not derived from quarried material, weathered out of the bedrock. There are some parts of the crystal mass which look to me like they have been weathered and polished, which would take a long time to do to corundum. This makes me think the specimen is eroded rather than quarried. With that in mind, maybe there are more!

The more I think about it the more intrigued I am with the possibility that some of the Howard county soapstone bodies may be serpentinite hydrothermally altered by pegmatite injection, similar to those in the MD/PA line area. Although pegmatites have not been mapped near most of these bodies, it is entirely possible they were not observed. For instance, the Henryton pegmatites are clearly seen on the 1928 Carroll County geologic map, but are absent on the 1993 Howard County map, right across the river. Did those dikes really do a dead-stop at the river’s edge? I don’t think so.

Contributed by Bob Conkwright

An Humongous Maryland-Collected Ruby Corundum

Weighing 16 pounds, and measuring 8 1/2 inches x 6 inches x 5 inches and pictured above is the most spectacular and amazing Maryland collected mineral specimen of thousands upon which I have gazed. Shortly after a 2009 visit to the Maryland Geological Survey's Baltimore headquarters on St. Paul St. to view its Maryland minerals on display, my friend Jeff Nagy inquired if I'd seen a gigantic Maryland corundum rumored to be there. Absolutely not: To the best of my knowledge, no Maryland-collected corundum specimens were known to exist.

Two and a half years later, Jeff called and invited me to accompany him to the MGS building for a visit with geologist Bob Conkwright, Jr., MGS Program Chief for Coastal and Environmental Geosciences. It turned out that for many years, this amazing specimen had served as a cherished doorstop in Bob's office.

Bob collected it circa 1960 at age eleven in the company of his father while collecting at one of the three long abandoned Devries Quarries in Carroll County. Once mined for feldspar, two of the Devries openings sit adjacent to each other along a bluff overlooking the Patapsco River near Hentryton. Bob explained:

"Start at the Henryton Tunnel and head downstream. The area was not as wooded back then, and there were just piles of dumps. I saw the weathered end of this thing sticking up and kicked it, hurting my toe. After a little digging, I first suspected it was some kind of hexagonal quartz cross-section."

About a week after our visit with Bob, my friend Harold Levey joined me on a short hike heading north up the railroad tracks along the Patapsco from Marriottsville looking across the river for a spot that could be where Bob made his find. Sure enough, about a hundred yards downstream from the Henryton Tunnel, the two openings remained. Although a few pegmatite rocks were visible on the ground, any dumps that may once have existed had long succumbed to fluvial forces and/or been buried with soil as the area has become heavily wooded. Even so, a few pegmatite rocks were visible. Now part of Patapsco State Park, prohibitions against collecting are actively enforced with inordinately costly penalties.

Open to question is whether this amazing piece was actually quarried from one of the openings upon whose quite shallow dumps Bob collected it. Could it have been loose in the soil/ saprolite layer, or even a product of blasting for construction of the Henryton Tunnel near the turn of the 20th Century? Bob Conkwright is eminently qualified to tackle these questions and has agreed to commit his thoughts to writing for an upcoming sequel to this post.

What is clear, however, is that this unique find from a half century ago makes a strong case that additional corundum is somewhere about. And fortunately, there's no law against checking out the various ever-changing alluvial deposits in and along the Patapsco as it heads downstream.

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.

Collecting at the LeFarge Quarry in Churchville, MD

The LaFarge Quarry in Churchville, Maryland, has become a popular field trip destination in recent years for mineral societies that have the proper insurance and whose members adhere to carefully stipulated safety regulations.

The collecting takes place along the berms on either side of two benches. Most of the rock is gneiss or metagabbro that can be boring to observe. But for the collector who knows where and how to look, it offers up a significant variety of minerals.

The quarry walls show occasional zeolite intrusions clearly visible from the benches below. On a recent trip sponsored by the Baltimore Mineral Society, several members uncovered and extracted some fine specimens of stilbite and chabazite from the berm beneath such an intrusion. They did so by attacking promising looking large boulders on the berms with sledge hammers and by turning over the smaller boulders and rocks amongst them. A significant find by any measure was the specimen displaying balls of stilbite crystals in the box at right,

Just as remarkable was a foot long vuggy vein of exquisite pseudorhombic pink chabazite crystals in another boulder beneath this same intrusion. Trimmed of a few hand specimens, the particularly impressive crystals remaining in the boulder appeared unlikely to survive further trimming on site without serious risk of damage. The circumstances prompted the seasoned and skilled collector who'd first spotted it to haul home all 25 pounds of the partially trimmed boulder that remained. Associated with the chabazite were a few small heulandite crystals.

Plucked as you see it at right from a point along the berm at least fifty yards beyond the zeolite veins in the quarry wall was the laumontite piece shown at right. Though a keeper, it falls far short of the best this locality has been known to produce.

Vugs in the rocks and boulders along the berms are scarce, and whenever noticed are worthy of checking out. One such vug yielded a pair of colourless and nearly transparent calcite crystals, each about 2 centimeters across, unusual for this locality. Another interesting find that someone told me about was an approximately one inch long mass of molybdenite in matrix. More typical finds included epidote in dark green blades up to about an inch as well as some transparent yellow-green micro-crystals. No doubt some clinozoisite was also collected, though none that I observed. And finally, as at just about every crushed stone quarry in the Maryland Piedmont, there was pyrite, mostly massive, sometimes in small octohedra, occasionally with associated minor chalcopyrite.

A "New Old" Baltimore County Locality

Call it "new" because there's little evidence that many people know about it. Call it "old" because my friend Harold Levey collected kyanite and staurolite here sixty years ago. The locality is on a hillside with extensive outcrops along the south bank of the Gunpowder River immediately east of the Paper Mill Road Bridge(s).

I can't think of another locality where garnets (var. almandine) are more prevalent than in the biotite muscovite plaglioclase-quartz schist that comprises these outcrops. Closer to industrial than gem quality and often quite weathered, garnets up to about an inch in diameter are everywhere.

Quartz that frequently intrudes into the schist, is what Harold recalls as the most likely matrix for kyanite. Typically bladed, he remembers finding it in loose rocks fetched from the ground. The season had been summer, and those rocks were not so hidden as they were today by a late November canopy of leaves. Otherwise, I suspect we'd have found some kyanite. However, we did come up with some staurolite.

This is probably he same locality that The Natural History Society of Maryland's 1940 publication, Minerals of Maryland , by Charles W. Ostrander and Walter E. Price, referred to as "At Ashland." The only other printed words were "In schist-kyanite, staurolite, and garnets."

We found the staurolite in the same schist that yielded all the garnets. The crystal bore the same almost gemmy luster as the ones Bob Simonoff encountered this past spring near Rockland. The fact that Minerals of Maryland listed no other Maryalnd localities for staurolite would lend further support that this was Ostrander and Price's "Ashland."

Very appealing about the locality is that by all indications, it appears to be collector friendly, so long as not swarmed en masse as a field trip destination, of which it should hardly prove worthy. Currently, parking for one car is available at a small pull-off immediately south of the bridge. When fishing season resumes, the space likely will be taken, or worse a no parking sign could be screwed to a metal post as one probably was at some point in the past. There are two slightly larger places to park not far down the road on the other side of the bridge.

The northern bank of the Gunpowder is similarly rocky. Harold recalls having prospected here as well, albeit to little or no avail.

Collecting at Sugar Grove, West Virginia

West Virginia? Aside from the meager Sugar Grove road cut locality in Pendleton County, I often wonder what else this state has to offer the mineral collector and why more information is not available. Considering the abundance of localities in all the states that surround West Virginia, such a dearth of mineral localities doesn't seem to add up. And certainly should not some of the geological activity that formed all those mountains left the state with more places to collect?

Pictured above from left to right at Sugar Grove are Robert Miller, Patrick Haynes, Maureen Campeau, and Stephanie Thi, all having a wonderful time breaking open chunks of basalt freed from the the shale into which they intruded millions of years ago. Therein are endless vugs which bear a variety of mineral species that can be quite spectacular when viewed beneath the scope.

Particularly notable is filiform pyrite, one of the most intriguing of this common mineral's numerous morphological forms. Filiform pyrite is has crystallized in the form of needles, which sometimes bend at right angles. Often at Sugar Grove, these needles are associated with the soft iron-rich clay silicate mineral nontronite, which can range in colour here from a light gray-blue to greenish black. At left is an example where the filiform pyrite has threaded dark spheres of nontronite. A right angle bent pyrite crystal coated with light bluish gray nontronite is shown at right. Microscopic pyrite crystals of other habits occur at Sugar Grove as well. Intergrown cubes are particularly prevalent

Chabazite (variety phacolite) is also notable amidst Sugar Grove's bounty. The larger crystals are easily identified. Smaller crystals that are visually quite similar to the phacolite, however are unfamiliar enough to stump me on visual identification. In the image at left, the larger 7mm. crystal to the right is obviously phacolite, but the smaller crystals to the left of it, I'm not so sure about. Included among them could be analcime and harmotome perhaps chabazite of a different habit, possibly even calcite, which is also common in these vugs, occasionally in the largest crystals of any species known to occur here.

Less common, but fun to find, is mesolite. Over three hours of cracking open rocks and peering with my loupe into vugs, the piece shown at right was the only mesolite that I, or to the best of my knowledge, anyone in our group came up with.

Though the collecting was better than expected, the locality was quite different than what I'd expected to find. It is an unremarkable looking road cut on the west side of Sugar Grove Road about 12 miles south of its intersection with Route 33. Needless to say, the area is quite rural. A possible landmark approximately 100 yards to the north on the opposite side of Sugar Grove Road is a couple of sheds, one with open sides, and a possible presence of a few old farming and/or construction vehicles and equipment.