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Etchison Mine, Montgomery Co., Maryland, USA

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Latitude & Longitude (WGS84): 39° 15' 19'' North , 77° 9' 22'' West
Latitude & Longitude (decimal): 39.25540,-77.15631
Köppen climate type:Cfa : Humid subtropical climate

Chromite mine worked in pre-Civil War times. The workings were largely bulldozed under a road in 1950.

Mineral List

6 valid minerals.

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

Cambrian - Neoproterozoic
485.4 - 1000 Ma

ID: 3190533
Precambrian-Phanerozoic sedimentary and volcanic rocks

Age: Neoproterozoic to Cambrian (485.4 - 1000 Ma)

Lithology: Metasedimentary/metavolcanic schist

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]

Early Cambrian - Neoproterozoic
511 - 1000 Ma

ID: 2456448

Age: Neoproterozoic to Cambrian (511 - 1000 Ma)

Description: Fine- to coarse-grained, lustrous, greenish-gray to gray, reddish-brown weathering, quartz-rich schist and much lesser mica gneiss. Contains interbedded metagraywacke and some calc-silicate rock. Typical mineral assemblages from west to east and from low to high metamorphic grade are: quartz-muscovite-chlorite-plagioclase-epidote-magnetite-hematite, quartz-muscovite-biotite-garnet-staurolite-plagioclase-magnetite?andalusite, quartz-muscovite-garnet-kyanite-plagioclase-staurolite-magnetite, and quartz-biotite-plagioclase-sillimanite-magnetite. Some sillimanite-bearing rocks also contain microcline. Cordierite has been recognized at a few places. Contains an abundant debris of ultramafic and lesser related mafic rocks (CZu)

Comments: gray, red brown; thin bedded; Dominant schistosity folation; chlorite, plagioclase, epidote; distal turbidite deposits in submarine fan

Lithology: Mica gneiss

Reference: Davis, A.M., C.S. Southworth, J.E. Reddy, J.S. Schindler. Geologic Map Database of the Washington DC Area Featuring Data from Three 30 x 60 Minute Quadrangles: Frederick, Washington West, and Fredericksburg. U.S. Geological Survey Open-File Report 01-227. [69]

541 - 2500 Ma

ID: 2928263
Wissahickon Formation (Undivided)

Age: Proterozoic (541 - 2500 Ma)

Stratigraphic Name: Wissahickon Formation

Description: Muscovite-chlorite-albite schist, muscovite-chlorite schist, chloritoid schist, and quartzite; intensely folded and cleaved.

Lithology: Major:{muscovite schist}, Minor:{quartzite}, Incidental:{schist}

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]

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.


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Gill, A.C. (1889) Notes on some minerals from the chrome mines of Montgomery County, Maryland: John Hopkins University Circular: 8 (75): 100-102.
Shannon, E. V. (1926) Mineralogy of the chrome ore from Etchison, Montgomery County, Maryland: American Mineralogist: 11: 16-20.
Singewald, J. T. (1928) Notes on feldspar, quartz, chrome and manganese in Maryland: Maryland Geological Survey vol. 12 part 2: 91-194.
Pearre, N. & A. V. Heyl (1960) Mineral deposits in serpentine rocks of the Piedmont Upland, Maryland, Pennsylvania and Delaware: U. S. Geological Survey: Bulletin 1082K: 707-833.

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