Pictured above at the long abandoned Tunnel Feldspar Mine in Howard County, are Maryland Park Service Supervisor for Patapsco Valley State Park Michael Burditt and Jeff Nagy. The latter's work continues regarding an updated revision of the 1980 Maryland Geological Survey publication Minerals of the Washtington, D.C. Area. Nagy located the Tunnel Mine by first researching literature written in the 1920's at the Maryland Geological Survey. Later, he reached the site after assuming that what today is a driveway appeared as "Tunnel Road" on a 70 year old map. The 1940 Natural History Society of Maryland publication Minerals of Maryland by Ostrander and Price also mentions the Tunnel Mine. Noted is how the adit "cuts into pegmatite rich in white potash feldspar." Located less than a mile into Howard County beyond Marriottsville, it is on land that the State of Maryland leases to active present farming interests.
The adit leads into a water-filled tunnel about 150 yards to the left as one heads up the driveway. Nagy does not know how far back it leads. Minerals of Maryland reports the occurrence of "white cleavage microcline, microcline crystals, a little mucscovite, biotite, and black tourmaline" at the mine. In the mica schist close by, were reported kyanite, staurolite, garnets, limonite psueudomorph after pyrite, and quartz crystals." Nagy has also perused literature from the U.S. Geological Survey citing the Tunnel Mine as a locality for beryl. But today, vegetation has long covered any dumps that may once have been, and the face of the cliffs near and surrounding the adit show little to attract collectors.
Interestingly, the available literature (unless we have missed something) shows the Tunnel Mine as Maryland's only feldspar mine. Less than a mile away, however, about hundred yards upstream from Marriottsville along the Carroll County bank of the Patapsco, is an adit leading into what obviously was another feldspar mine. The Maryland DNR Trail Guide has even mapped this adit as a cave. Water has not invaded it. Nagy ventured inside in 2010 with Maryland collector Fred Parker and a reporter from NPR to broadcast a story about the mine's existence. Nagy recalls the opening reaching back approximately 300 navigable feet.
Based on personal visits to both localities, as well as input from Jeff Nagy and Fred Parker, the likelihood of finding collectible minerals at either locality is slim at best. Regardless, laws prohibiting collecting in the Patapsco Valley State Park are rigidly enforced. Breaking them entails theft of State property. Access to see the Tunnel Mine would require permission from the active farmers who rent the land as well as the Maryland Department of Natural Resources. The adit along the banks of the Patapsco near Marriottsville Road, however, is accessible to the curious, all the more so during seasons when the surrounding vegetation is minimal.