Being both a bicycle and monument enthusiast, recently I have been combining the two and taking a self-guided bike tour of my hometown, Washington, DC. Just for kicks I am putting together a personal collection of pictures of my bike with the monuments. Though I see the monuments often I still enjoy them and appreciate getting to share them with people for the first time. Yesterday I made my way over to a few memorials including the FDR Memorial along the Tidal Basin. I remember when this particular one opened up and enjoying it because it is a collection of waterfalls and statues, and that it brought a different approach than the other monuments in DC. While there, a few of the rocks found in the walls jumped out at me; in particular this pegmatite dike.
*Bike as a sense of scale borrowed from Alan at Not Necessarily Geology
While the surrounding parent rock is pretty evenly distributed between minerals this dike is visibly dominated by feldspars, most notably the bright pink orthoclase. The other mineral looks to me like plagioclase with a green tint to it. I felt it might be frowned upon to scratch the memorial, but the two cleavage planes are apparent. Below a crystal of plagioclase has fractured and infilled with quartz.
Unfortunately I don’t know the locality where this rock was taken from, but I can appreciate the unique aspect and added beauty it brings to the memorial. Keep an eye out the next time you are visiting the monuments maybe there are some other hidden geologic gems to be found, and if you want a tour send me a message I am always willing to take another ride around the city.
