Here’s an assortment of serpentinite from the Serpentine Prairie. The first three show the polished surfaces that form so easily on this soft rock type, as well as the variety of blue-green colors. Remember, serpentinite is a metamorphic version of peridotite, the deep-seated, low-silica rock that forms the upper mantle and the bottom of oceanic plates.
Darker bits may reflect more iron-rich protoliths, or maybe rocks that are less altered.
And remember, no collecting in the park. If you like serpentinite, do what I did and collect from the roadside just to the west of the park, or down in the Crestmont neighborhood.
Oakland Geology 
11 July 2009 at 12:45 pm
Michele, have you looked at the Delaware geologic map on my About.com site? The larger versions list serpentinite as part of the Wissahickon Formation, which is upstream in northernmost Delaware.
11 July 2009 at 4:18 am
I am so glad I found your site! My boyfriend and I live in New Castle, DE near Battery Park. The park is adjacent to the Delaware River, and the ocean is not far away. We had found all of these beautiful green rocks on the beach and took some home for our rock garden. We had no idea what kind of rocks they were, but we liked them. Since I found your site I know what they are and where they came from. Thank you for all of your information and pictures.