Monday, June 14, 2010

Collecting at the Havre de Grace Quarry

Hats off to the Vulcan Materials Company/Arundel Corporation, except for hard hats that is. Assistant Plant Manager Patrick Pieton couldn't have been more gracious when he opened up the Havre de Grace Quarry on a recent Saturday for Baltimore Mineral Society members to collect.

The quarry descends from 670 acres immediately south of the Susquehanna River and west of Havre de Grace at a point where the Port Deposit gneiss meets Harford County's metagabbro and amphibolite. It is visible off to the right as one drives north across the Susquehanna on I-95. Although the rocks are hard, they bear plenty of mineral specimens that are relatively easy to collect.

After an informative briefing from Pat about the quarry and mine safety, we followed him in our cars down several levels to collect along berms on either side of road. Sulphides proved to be abundant in the rocks here, especially pyrite in large masses and sometimes in cubes up to at least an inch. Unfortunately these crystals were impossible to extract from the much harder gneiss and metagabbro encasing them. Often associated with the pyrite were less sizeable masses of bright yellow golden chalcopyrite sometimes accompanied by wildly iridescent bornite. One of the more interesting finds was a sizeable mass of pyrrohotite running through a matrix bearing few small particles of what through the loupe appeared to be crystalline sphalerite.

Excitement increased when Fred Parker found a large boulder partially coated with a druse of clear colorless zeolites. Through the loupe, we were able to identify heulandite for sure, and very possibly some chabazite as well. The druse, however, was of a different hue than a particularly attractive 1988 heulandite find by Parker where the micro crystals were orangish brown and occasionally accompanied by slightly larger crystals of white calcite.

Collecting only got better when Pat reappeared to lead us to the bottom level of the quarry. Within minutes we were in the midst of numerous rocks coated with heulandite druses of similar hue to those from the 1988 find. Although mostly quite weathered, occasional scatterings of micro pyrite cubes contributed a dramatic sparkle to some of them. The image at right was shot at 40x.

Also present at the same spot were some rocks covered with bladed sprays of white laumontite. After whacking one of them with my mallet, two attractive small cabinet sized slabs broke off to expose laumontite on both sides. Nearby, Bob Eberle pounded away at a boulder from which he ultimately extracted an attractive epidote crystal of approximately an inch. As abundant as epidote is likely to be in this kind of rock, it was the only such find of the day.

As our noon deadline approached, Fred Parker wondered off to what was probably the day's piece de resistance. Quite apart from where we'd been collecting, it was an enormous boulder he'd spotted soon after our arrival at the bottom level. The druses of orange heulandite covering it were less weathered. After pounding away at the boulder with a sledge hammer he inserted a small chisel at a point where one crystal coated slab after another soon detatched. As he wrapped the pieces in newspaper and placed them into a compartmentalized flat, several of us ran off in yet another direction from the spot where we'd spent nearly all of the past two hours. Almost too much heulandite, it seemed, not enough time.

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