Friday, December 9, 2011

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.

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