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.

1 comment:

  1. David S. BernsteinApril 16, 2012 at 3:46 PM

    I enjoyed your article. I took the picture that appears in Minrec and to which you refer. I loved my trip to Woods and look forward to heading back there one day.