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The group went on to take samples of rocks that are part of the Baltimore Mafic Complex, a band of intermittent outcroppings that extends from the metropolitan area northeast to the Pennsylvania line and was involved in the formation of the Appalachian Mountains.

Today, some 419 million tons of this and less alkaline “mafic” wastes are produced annually.

In particular, the materials contain mafic components that seem to be dominated by a mixture of olivine and low-calcium pyroxene.

This stuff is composed of sideromelane, a basaltic glass formed when mafic lava is quenched suddenly in water; some tiny wee pillows; plus palagonite and some other assorted things, all welded together into a solid mass.

This marvelous mafic rock formed a thick sill above the soft sedimentary layers, and cooled slowly deep underground.