Hunting Hill quarry (Rockville Crushed Stone Quarry; Travilah Quarry; Rockville Quarry; Bardon Stone Quarry; Aggregate Industries Quarry), Rockville, Montgomery Co., Maryland, USA
|Latitude & Longitude (WGS84):||39° 5' North , 77° 9' West|
|Latitude & Longitude (decimal):||39.08333,-77.15000|
|Köppen climate type:||Cfa : Humid subtropical climate|
A large active quarry (as of December, 2013) in the Ordovician-age Hunting Hill pluton. The pluton in the quarry is thought to be originally a dunite, now largely serpentinized. Gabbro dikes cutting the serpentinite have been converting via metasomatism to rodingite, a mixture of calcium-rich clinopyroxene (here a green chromium-rich diopside) and a pink to white grossular garnet. Shearing along the contacts between the more resistant rodingite and the weaker serpentinite as well as within the rodingite has provided space for veins and open-space fillings of a suite of bizarre often well-crystallized minerals. Over 60 minerals have been reported so far from the quarry, according to the excellent article by Parker (2005). Notable finds are red gemmy grossular crystals, coalingite masses, desautelsite, prehnite crystals, mcguinnessite and calcite crystals.
59 valid minerals.
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 Macrostrat.org
|Early Cambrian - Neoproterozoic|
513 - 1000 Ma
Lithology: Vein quartz
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. 
541 - 2500 Ma
|Wissahickon Formation (Undivided)|
Age: Proterozoic (541 - 2500 Ma)
Stratigraphic Name: Wissahickon Formation
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. 
Bernstein, Lawrence (1980) Minerals of the Washington D. C. area: Maryland Geological Survey Educational Series 5, 148 p.
Parker, F. (2005), The Minerals of the Hunting Hill Quarry, Rockville, Maryland; Mineralogical Record 36 (5): 435-446.