Tuesday, February 28, 2012

Uncommon Finds in Harford County, Maryland

Recently, an email came in from a Mineral Bliss
reader named Deb who lives near the northwestern corner of Harford County, Maryland. She said she had found microscopic flakes of gold in a nearby creek. She also reported having collected a large ilmenite specimen amidst rocks directly across the road from her house. Rutile, she said, is "everywhere out here." Deb was born in this area. She has lived hereabouts most of her life and collected minerals since childhood. Needless to say, I was intrigued and promptly made arrangements to visit.

Shortly after my arrival, Deb suggested we go for a drive. Heading east on Maryland Route 136 , we drove through an area where quartz had frequently intruded amidst late Precambrian Upper Pelitic (Wissahickon?) schists. The quartz hosts all the ilmenite of which Deb had spoken and once hosted the rutile crystals, most of which have separated and typically occur loose in alluvial deposits and plowed fields. Regarding the latter: "Some fields have a lot of rutile,"Deb explained, and some don't have any." She drove me by a cornfield very close to the Pennsylvania Line where the owner had given her permission to collect. Though mostly covered with remnants from last summer's crop, enough stones were visible for us to pluck a few rutile crystals and two pieces of ilmenite with quartz.

The geology in this part of Harford County is fascinating. Farther east on Route 136 near Whiteford, Deb pointed out woodlands to the north that host a large opening that was once the Williams Slate quarry. Circling the immediate area of this opening , a geologic map of Harford County shows a ring of rock referred to as the Volcanic Complex of Cecil County. I surmise that the site of the old Cardiff Serpentine Quarry, once noted for its Verde Antique building stone, sits somewhere within the boundaries of that ring about a mile farther north at the Pennsylvania line.

We continued driving east on Route 136, passing the crossroads of Dublin, from which a short road leads to sites where talc was once quarried in large steatite openings. Uncertain regarding accessibility, we continued southeast on Route 136 for another mile to Route 1. There we turned left, and headed northeast across the the bridge over Conowingo Dam into Cecil County. Near Conowingo, Deb quickly led me to a spot where we found a small piece of rhyolite from that county's aforementioned and eponymous Volcanic Complex. Though the country rock here was Port Deposit gneiss, the origination of rhyolite pieces sparsely scattered on the ground been traced to a location within Cecil County's scattered Volcanic Complex somewhere between here and Northeast, Maryland. It was my first encounter with Maryland rhyolite.

From here we headed back to Deb's house where she had yet more that was interesting to show me. In a vial with those sparse flakes of gold she had panned from the stream near her house was a silver coloured nugget, measuring a fraction of a millimeter, that looked like platinum, which would certainly be very unlikely. Having since taken time to study its photomicrographic image, however, it screams micrometeorite! We're eager for word from any readers with different ideas.

In a lifetime of collecting, Deb has come up with a lot of interesting material from other parts of Harford County. Though hardly known for its pegmatites, Deb was at hand about 20 years ago when the construction of a driveway uncovered a small pegmatite outcrop within a mile of where Route 1 crosses Deer Creek. It was here that she collected the beryl crystal pictured at left, the only example of the species that I've seen from Harford County. The same locality also yielded the specimen at right, which appears to be two columbite crystals in feldspar. Assuming a correct visual identification, this is not only the sole columbite I've encountered from Harford County, but from anywhere in Maryland. Deb also collected the chalcedony pictured at left from a spot close by where the local rock was metagabbro.

Finally, and again at least several decades ago, Deb uncovered an amethyst crystal on a long since built over farm on the south side of Route 1 very close to where it crosses from Harford into Baltimore County. Although the Natural History Society of Maryland's 1940 Minerals of Maryland publication by Ostrander and Price reports amethystine drusy quartz from Mine Fields, this is the only find of an actual amethyst crystal that that I'm aware of from Harford County. Since her crystal was marred with its share of dings, Deb had cut from it the pendant pictured at left next to the remains of the original crystal.

Interestingly, all of the species Deb has found that seem so unusual for Harford County are present not far across the Mason-Dixon Line in Southern Pennsylvania, where the Piedmont geology is relatively similar. It should also be safe to say that Pennsylvania, over the years, has attracted a lot more collectors to uncover them.

1 comment:

  1. Nice! I have always wondered if Rutile could be collected still in PA cornfields. I have never done so and live too far away to make hard attempts to do so. I wish I lived in the area and could ask everyones permission before farmlands turn into subdivisions.