Friday, May 11, 2012

Baltimore City Diggings at Herring Run

Nearly every day for eight years during a much longer than eight year hiatus from mineralogical pursuits, I walked  the paved loop on either side of Herring Run between Harford Road and Belair Road. Even though these walks were for no purpose other than exercise and the enjoyment of being outside, had there been much of mineralogical interest along the way, I probably would have noticed.  Except for the alluvial deposits in the stream, this stretch of Herring Run Park was all mica schist that was so boring I don't recall  ever noticing any other rocks or minerals associated with it.

 Having moved on to other means and places for daily exercise and outdoor activity, ten years passed without my even once visiting the park again. Prompting me to return recently were digging and blasting to replace aging and decrepit sewer pipes that run adjacent to the stream.  To reach the above pictured spoils from it by car, take the spur extending southwest from Harford Road immediately south of its intersection with Argonne Drive. Park where the spur ends, walk under the bridge along the north bank of Herring Run, and you'll be there.

As expected, most of the rock here is the same boring  mica schist. Associated with it, however, are  intrusions of  feldspar and massive smoky quartz. Most interesting of the latter two is the feldspar, some of which is  attractive enough to be collected in its own right, as shown at left.

Most of the  feldspar, however, is lighter in colour and  more coarse. Often it occurs in combination with the mica schist and the smoky quartz.  These rocks are often the most interesting  to break open and explore.

The schorl crystal shown at right measures 3 cm. x 1.8 cm. and was one of the smallest, albeit easiest to dislodge schorl crystals in the larger rock from which I trimmed it. That's the good news. The not so good news is that very few rocks  I observed bore any schorl.

Garnet, which I assume to be almandine, is more likely to be inside  this rough feldspar material. The chances of finding or  extracting an unbroken crystal of significant size could be slim. However,  the  colour and luster of these garnets are notably gemmy.

I'd be surprised, to find any other mineral species at this locality. None of the material here is vuggy, and examination of it under the scope has revealed nothing of interest. Still, it's a spot in Baltimore City, that for now, at least when the workers are not present---think early evening and weekends--- should probably be all right and perfectly safe for collectors to crawl around in the dirt  and hammer away. And undoubtedly, further blasting in the future will take place downstream to provide additional  material to check out.

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