Saturday, March 27, 2010

Some Dazzling Maryland Microminerals

This week's post borrows from a brief slide show of Maryland micromounts that I presented this past Friday evening to the Atlantic Micromount conference. Regular followers of Mineral Bliss may have seen some but not all of these specimens before. The cover girl is anglesite from Frederick County's Mountain View Lead mine, photographed at about 30x. The smithsonite image at left, shot with similar magnification ,also hailed from the Mountain View locality. Its colour amazes me. Both specimens were collected about 15 years ago. The self-collected azurite with malachite at right is from my visit there that was described in the Mineral Bliss post of March 21, 2009. It was the only evidence of either of those two secondary copper minerals I encountered.

The much more more spectacular malachite (left) was collected in Carroll County just east of Frederick County at the Lehigh-Portland Cement Quarry near Union Bridge. Most of Maryland's relatively scarce crystallized malachite occurs in acicular crystals. Their different habit and greener than green hue against a backdrop of yellow calcite makes them a personal favorite. The colour of this calcite isn't too different from that of the only wulfenite ever reported from Maryland, which interestingly was collected at this same Lehigh-Portland Cement Quarry locality. All that was ever found was from a single rock uncovered in the 1970's by the late and legendary Maryland collector George Brewer. A flattened pyramid of this wulfenite is pictured at right. Just above it is a cerussite crystal that measures about a millimeter.

The Maryland cerussite crystals below at left are much larger, but not so much so as to preclude being shown in the company of microminerals. They were also collected in Carroll County just a few miles away at the Redland- Genstar Medford Quarry. Though displayed in my collection as a hand specimen, the crystals are better appreciated with the magnification from a macro lens as shown. The rarest and most remarkable mineral ever yielded from the Medford Quarry is the lanthanite pictured at right. As with the wulfenite that was found so close by, all of Maryland's known supply of lanthanite came from one rock. While the nomenclature system for such rare earth species directs that the dominant rare earth element's symbol be shown at the end of the mineral's name, I do not believe such a determination was ever made with this find. A good reason could be that it was too dear and tiny to give any up for testing.

Though Maryland has more than its share of zeolite localities around the state, I'm not aware of any that have produced micromounts more eye-catching than the old-timer chabazite and heulandite pieces that are in Harvard University's micromount collection. Both specimens were from one of the several long closed and covered up 19th century gneiss quarries that operated in Baltimore City's Jones Falls Valley. The chabazite is at left, the heulandite at right.

Maryland's serpentine barrens, all which were once mined for chromium, have also yielded some intriguing micromount material. I feel like apologizing to those who attended my presentation this past Friday night for neglecting to show them the chromian clinochlore (aka rhodochrome, penninite, japanite, miskeyite) pictured at right from Cecil County's State Line Chrome Pits and part of the Harvard collection. The kind of beautiful red quartz crystals at left from the geologically similar Soldiers Delight in Baltimore County are less likely to occur within the vast expanses of serpentine barrens than lining vugs in rocks from its greener wooded areas. Though the land is public and has been set aside for the enjoyment of all, the the removal by anyone of mineral specimens is strictly prohibited with enforcement that's known to be rigid.

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