Greensburg Quarry (McMahon Quarry), Valley Stream, Baltimore Co., Maryland, USA

Ref: Minerals of the Washington D.C Area.

Operated for crushed stone by Arundel Corporation of Baltimore.

In gneissic facies Cockeysville marble (calc-gneiss, scattered layers and lenses of calcite marble). Pegmatite and small quartz veins are common and a fine-grained mafic dyke (high proportions of ferro-magnesian minerals; mostly amphiboles).