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McMahon Quarry (Greensberg Quarry), Bare Hills, Baltimore Co., Maryland, USA

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Latitude & Longitude (WGS84): 39° 22' 59'' North , 76° 41' 30'' West
Latitude & Longitude (decimal): 39.38307,-76.69154
GeoHash:G#: dr12nc6yv
Locality type:Quarry
Köppen climate type:Cfa : Humid subtropical climate

A quarry located near Bare Hills, Cockeysville area, and operated for crushed stone by Arundel Corporation of Baltimore.

The quarry is in a gneissic phase of the Cockeysville marble (calc-gneiss with scattered layers and lenses of calcite marble), intruded by a numerous small pegmatites, quartz veins and a fine-grained mafic dyke (high proportions of ferro-magnesian minerals; mostly amphiboles). It was operated for crushed stone by Arundel Corporation of Baltimore.

Mineral List

19 valid minerals. 1 erroneous literature entry.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

541 - 2500 Ma

ID: 2717167
Cockeysville Marble

Age: Proterozoic (541 - 2500 Ma)

Stratigraphic Name: Cockeysville Marble

Description: Metadolomite, calc-schist, and calcite marble are predominant; calc-gneiss and calc-silicate marble widespread but minor; thickness about 750 feet.

Comments: secondary unit description from USGS Geologic Names lexicon (ref MD004): Author has erected a six-fold stratigraphy for the Cockeysville consisting of five unnamed members and one lens to accommodate the variety of rock types. These are the layered marble member (0 to 200 m), the massive metadolostone member (0 to 400 m), the layered metadolostone member (0 to 1.4 km), the massive metalimestone member (0 to 450 m), which includes the calc-gneiss lens (0 to 225 m), and the phlogopitic metalimestone member (0 to 300 m). Each member is described in detail. Thickness of the Cockeysville overall varies from 0 to 1.4 km, the range of the layered metadolostone. The relative ages of these units are uncertain. Unit as a whole is mapped as Cambrian to Ordovician(?).

Lithology: Major:{marble}, Minor:{calc silicate schist}, Incidental:{calc silicate gneiss}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

1000 - 1600 Ma

ID: 3193072
Mesoproterozoic crystalline metamorphic rocks

Age: Mesoproterozoic (1000 - 1600 Ma)

Lithology: Orthogneiss

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Anonymous (1935): Rock and Minerals Association third outing. Rocks and Minerals 10(7), 110.
Jones, A. L. & W. E. Price (1937): R & M A outing in Maryland. Rocks and Minerals 12(10), 247.
Ostrander, C. W. & W. E. Price (1940): Minerals of Maryland. Natural History Society of Maryland , 92 pp.
Bernstein, Lawrence (1976): Minerals of Washington D.C. and vicinity. U.S. Geological Survey Open-File Report 76-849, 183 pp.
Bernstein, Lawrence (1980): Minerals of the Washington D. C. area. Maryland Geological Survey Educational Series 5, 148 pp.

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