Saturday, October 3, 2009

Word from Harvard about Bare Hills Chromite and Magnetite

A month ago, Mineral Bliss posted observations related to Maryland minerals at the Harvard Mineralogical Museum. Of particular interest was a small exhibit of chromite in various habits from different localities. Two of the selections were from Bare Hills in Baltimore County. One was massive chromite with fibrous serpentine. The other was the glass vial pictured above at center filled with minute octahedra about which my comments were as follows:

I would love to know how these crystals were collected. Did they occur as floaters in the soil, or were they extracted from a (presumably serpentinite) matrix? Although massive chromite has always been ubiquitous at the Bare Hills serpentine barrens, crystals are most unexpected.

That expression of curiosity would have been the end of it had not my friend Harold Levey (at left) telephoned to share further thoughts. To Harold, whose collecting experience at Bare Hills spans more than 70 years, the likelihood of chromite crystals having been collected at Bare Hills was every bit as remote. He also emphasized the visual resemblance of the crystals in the jar to magnetite crystals that were ubiquitous on the long built over dumps of the Bare Hills Copper Mine.

Still in my possession are the magnetite crystals pictured at left of the jar that I collected at the Bare Hills Copper Mine myself more than 50 years ago. They typically occurred as pictured in a talc-like steatite soft enough for one's fingernails to dislodge. In appearance they resemble chromite crystals. Pictured at right of the jar is the only example immediately available for me to photograph of crystalized chromite (a micromount from Gabon, actually) . MINDAT has numerous better examples.

I was wary of challenging the identification of anything displayed in such a world class museum. However, encouraged by Harold to do so, I mailed off a letter to its curator, Dr Carl Francis suggesting the possibililty of a discrepancy.

Just two weeks later, a return letter arrived from Dr. Francis. He had researched the history of the specimen and even found its original label from the Leonhard Liebener Collection, which was
purchased in Austria in 1869. While the information on the exhibit label had been correctly transcribed, the crystals, when confronted with a magnet, were mostly magnetic octahedra accompanied by "some rounded black, nonmagnetic (chromite?) grains. " I conclude," Dr. Francis wrote," that the specimen is a mixture that was accepted as chromite by Liebener and hasn't been questioned until your recent visit. I have relabeled it magnetite, attributed it to the Bare Hills Copper Mine on your authority, and retired it from the display."

Thank you Dr. Francis for going to such lengths upon hearing from the likes of Yours Truly, and thank you Harold Levey for the observation that inspired in me the gall to write. As a bonus, Dr. Francis shared additional information about Maryland Minerals owned by the Harvard Museum that are not currently on display. We're hoping for the opportunity to share related information in the coming months.

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