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.