Saturday, March 31, 2012

Mineralogical Ramblings in Cecil County, Maryland

Threats of an earlier than usual presence of briars, ticks, and snakes this spring of 2012 prompted me to spend an inordinate amount of time the past couple of weeks searching for minerals in rocky and wooded areas. Much of the focus has been in Cecil County, Maryland, on either side of of Pilot Town Road and Pleasant Grove Road as they approach the the Mason-Dixon Line.

Though most of the land hereabouts is stringently posted, it is dotted with abandoned quarries, prospects, and pits once variously worked for talc, feldspar, chromite, and serpentine. Most mineralogically significant of these were the State Line Pits, of which the dumps are now buried beneath earth overgrown with briars. Though this locality produced Maryland's finest williamsite in years past, it's long been inaccessible. The most recent attempt to collect at the State Line Pits of which I'm aware was by an accomplished collector who gained access to the site 18 years ago and after digging extensively, returned home skunked.

After having gained permission to visit the sites of other long abandoned and grown over workings in this part of Cecil County, I've concluded that the best place in to look for the greatest variety of interesting minerals is in the area's more accessible alluvial deposits. In the Pilot Town Road vicinity, my recommendation would be Conowingo Creek immediately north of the bridge where the Pilot Town Road bridge crosses it.

The most collectible species here are chalcedony and jasper. To spot them, look for rocks with dark, rough, and mangled surfaces, then break them open if necessary to be certain. Any green rocks, of course, are serpentine. Much of the serpentine that was mined in this immediate vicinity and thus most likely to turn up in alluvial deposits is of the verde antique genre, which is wonderful as a building stone, but should bore most collectors. More collectible and interesting serpentine is readily available in the ubiquitous roadfill hereabouts that's quarried from Lancaster County's Cedar Hill Quarry or Penn-Maryland Quarry

To find a piece of serpentine, variety williamsite,
however, would be another matter. Alluvial deposits along Octoraro Creek or its tributaries should offer better odds as they flow closer to williamsite localities, mostly in Pennsylvania, that have produced the greatest quantities of this dear and cherished species. I've not yet explored the Octoraro deposits, but was standing by recently when a collector pulled the amazing piece at right from an Octoraro tributary just a short distance north of the Pennsvlania line.

Pebbles of reddish quartz or quartzite, especially with vugs or holes that could once have encased crystals, are worth a whack with the hammer. The red colour is from iron, which could signal a presence within of sulphides, namely pyrite, chalcopyrite, goethite pseudomorph after pyrite, or magnetite. Particularly interesting was the specimen at left. It is from inside a larger and less water polished, but otherwise similar rock in nearby field we visited after leaving the alluvial area. Note how it bears goethite pseudomorphs after pyrite crystals immediately next to pyrite that had not so much as tarnished.

Also curious was the shiny white material that appeared when I broke open the Conowingo Creek alluvial quartz pebble pictured at right. For all the world, it looks to me like brucite. Though indigenous to the region, brucite is not a species I would expect to uncover when breaking open a piece of quartz. Even after examination under the scope, I don't have a clue.

Finding corundum amidst these thousands of rocks would seem more likely. Having recently searched for it to no avail in alluvial material along the Patapsco River near Henryton in Carroll County, MD, corundum was on my mind. That, of course, is where Bob Conkright made the corundum find of his life. There as in this part of Cecil County, the abundant presence of talc, feldspar, quartz, and serpentine in close proximity create the right environment. Considering reports of corundum nearby along the Nottingham Turnpike just 1 1/2miles northeast of Chrome, PA, and with hundreds of tons of corundum having been mined during the 19th Century at various geologically similar locations in neighboring Chester County, PA, why not?

Monday, March 12, 2012

The Wood's Chrome Pit Today

First of all, to properly learn about this classic Lancaster County, Pennsylvania locality near the Township of Little Britain and very close to the Maryland Line, one should read Wendell Wilson's article in Mineralogical Record, July-August, 2011, Volume 42, Number 4. It even has maps showing the location.

Conveniently for the very nice property owners, this edition of the periodical came out at a time of year when enough copperheads and poison ivy were around to discourage any onslaught of collectors.

Notwithstanding MinRec's maps, or even if using GPS, the locality is not easy to find or reach. Only through the kindness of a collector who had previously visited the Woods Mine and understood the necessary protocol for gaining access and permission to collect did I manage to get in. The collecting takes place on dumps surrounding a water-filled pit.

These dumps are numerous and all worth checking out. A picture in MinRec shows one area where in 2010 a backhoe had overturned new material. Notwithstanding, I enjoyed my best luck on dumps that appeared to have withstood the ages.

MinRec's images of Wood's Mine specimens practically render its author guilty of understatement for noting that "none of (the more recently collected material) rivals the specimens found prior to 1881." That was also the year the mine closed. On the other hand, numerous minerals worthy of collecting remain. Still abundant and occasionally of quality sufficient for display is the reddish eggplant coloured chrome antigorite, (var. picrolite), such as pictured at left. The same can be said for rich massive chromite, as shown at right. With a bit of luck, I suspect that one might still find a piece of chromite coated with traces of the deep emerald green nickel carbonate zaratite. It interested me, however, to note recently on MinDat, that the IMA status of this much cherished by collectors species was "questionable."

Even more questionable is the bright and colourful nickel-bearing material known as garnierite, which MinDat refers to as "the result of lateritic weathering of ultramafic rocks (serpentinite, dunite, peridotite)--- mostly a mixture of various nickel and nickel-bearing magnesium layer silicates." I've also encountered it labeled as deweylite when in association with white magnesite as shown at left. My hunch, however, is that one with better knowledge of the Wood's Mine and its species would simply refer to it as antigorite.

I'm not aware of a species that assumes more forms, colours, varieties, and names than antigorite. One that's unmistakable as well as the creme de la creme of the antigorites, is williamsite. Prized by jewelers and carvers, its transluscence and a presence of chromite specks within are what distinguishes it. Albeit a scrap, I consider myself fotunate to have uncovered the thumbnail sized piece at right.

Of all the different species for which the Wood's Mine is known, the world- class brucite specimens collected there in the mid-1800's brucite are the most famous. Brucite sufficient for reference can still be found on the dumps, though it is not abundant. The best I could come up with is the very weak example (shiny material) in the image at left. Another once abundant species that I feel certain is also still around is kammererite, penninite, rhodochrome, chromian clinochlore, or whatever other name one has for it. I found but specimen that arguably bore traces of such material. The other side would proclaim the little piece I found to be chrome antigorite. Especially in very small quantities, it's easy to confuse the two. Kammererite is distinctly micaceous.

The Wood's Chrome Mine is but one of numerous localities amidst serpentine barres that cling the Maryland-Pennsylvania Line. All that are accessible should prove worthy of a visit.